To sum up :
— You’re saying that the higher level you are, the better you are at knowing what skills belong to what league (but not necessarily at noticing when being matched against).
— Nordy and I do state that the lower level you are, the more keenly you will feel if you’re playing an user above your level (but not necessarily at knowing from which league they are from).
It seems to me that those propositions aren’t mutually exclusive. 
Alright, back to the main course :
SMURFS REPORT W33-35
SILVER LEAGUE
Using a randomized procedure (similar than for the gold league) :
How to read : cf. first post (part II)
Method used : cf. dedicated post.
Quickie :
Over 105 users at silver MMR :
Some thoughts about this :
FUN FACTS
Now for the funny part :
Once upon a time, was a lad known as « Ok ».
Ok was a high league player, but stagnated. So, one extremely gloomy day, he decided to stop playing in diamond 1, and to freelose 1000 MMR+ in order to feel like the man again. And it worked wonders, he finally could get the 20-30 games winstreaks he had always dreamed of. By continuously slaying unsuspicious lower leagues, he felt he had regained his virility. He felt like a Flash among the men.
But good things aren’t meant to last. One Saturday in the evening, he was matched against another lower league player, that we will call Pony. Ok didn’t noticed, but the pony seemed shaken by his manly apparel, as if he had seen a ghost.
Full of confidence, Ok deployed a splendid exemplary of skill : with his 235 APM, he hit every macro timing magnificently. He even killed the opponent’s scout who was trying to harass his CC building SCV. Such a foolish attempt !
But upon preparing to lay waste on the pony’s mineral line, Ok noticed the wall was made with three supplies. Suddenly, he didn’t feel ok anymore. An alert immediately sounded : his base was being assaulted by a small squad of marines, and they weren’t friendly. Listening only to his 200+ APM fingers, he got back, and tried to temporize an SCV pull. But while doing so, the second Pony’s SCV had (barely) had the time to land a bunker. He had just lost the game to a vulgar pony. And Ok wasn’t ok with that at all : he did ragequit, and by that had his first real lose in a while.
What was the difference between the pony and the 20 previous players ? Skill ? Nah, otherwise the pony wouldn’t belong to an intermediate league. It was information, as contrary to the others, the pony had learned to recognize smurfs right away.
Moral of the story : would the devs let the ladder be ruined by smurfs, we regular players would still have a chance to deal with them by ourselves. Know your enemy, goes the saying. Even more so in a strategy game.
PS : first post updated. See you in about three weeks for Bronze league ! 
And here we go for Bronze :
SMURFS REPORT W36-38
BRONZE LEAGUE
Still with the randomized procedure :
How to read : cf. first post (part II)
Method used : cf. dedicated post.
Quickie :
Among 105 users at bronze MMR :
Some (important) thoughts about this :
Corrected by league’s population, there would be :
This is the estimate I will retain from this report. 
FUN-FACTS
FINAL THOUGHTS
That’s it folks, I said I wanted to survey the 4 metal leagues, and after many weeks, the objective is complete. I must say that task required for me to get knowledge and tools I didn’t have a first, and that coupled to the hints I had to define, and the hidden nature of my targets, I sometimes felt like some kind of secret service analyst (lol). Anyway, it was an intellectually stimulating challenge.
Lastly, the previous report didn’t raise any reaction. However, with it the thread did attract lots of views (more than 320), and that even while being in the abyss of a three weeks inactivity. That’s remarkable, and I can only hope some of the eyes apparently so interested were those of the devs. If you guys ever read this : don’t assume F2P won’t bring to SC2 what it did to LoL. Don’t let smurfs ruin the game from beginners to intermediate levels, or you will lose the former.
Now, of course it could be interesting to survey the diamond and masters leagues, possibly to redo platinum. I could also do a best-of about the hints you could get to spot a smurf on the loading screen. And I’ve got something about the different motivations behind smurfing that might interest the devs.
But some views on a thread, without comments, without likes, and with the blue ones remaining ever silent on the matter, aren’t enough to renew my motivation. So unless there’s some change, I can let my work as is. I will still wander around to exchange as any other community member though. And, since I’m now trust level 3, will use the opportunity to transform the first post into something really neat. 
See you around, folks !
Concerning Leaver botter on EU where a smurfer ruins my RT games by leaver/afk botting
They did delete and lock all the posts in that thread except the first two, so either because of the replays or something else happened after I went to bed
I didn’t get any suspension, but it shames me I can’t even discuss leaver botting. The account name of the person was removed from the thread. Massively grieving other players should be punished, not ignored and censored when it’s reported. You disappoint me, Blizzard
Told you there should be nothing linking to the individual himself ; otherwise he could be targeted by the most angry readers. I might add that there are a lot of users around here who don’t see with a keen eye when their doings are denounced… and so if the smallest rule is broken in the process, they will report it so that the author gets silenced.
Now, you can’t denounce that individual ; but we can still discuss the case without breaking any rules. And that by debating over the phenomenon in general ; and anonymizing any source material.
I took a look at it, and I must say this user’s procedure was quite unusual. However, after careful inspection, I’m not sure there is botting involved, and I’ll explain you why below :
First, the profile :
https://i.postimg.cc/bYQR8bYq/2020-10-04-AFK-smurf-Profile.jpg
Ingame :
https://i.postimg.cc/Bnhgk0SD/2020-10-04-AFK-smurf-ingame.jpg
From the whole analysis, we can deduce that :
So my conclusion is that he’s there at the beginning of some games for sure, but not all, while the games’ ends look somewhat automated. So I can’t rule out an external program, particularly for the end.
As for the why, well it’s made to lower his MMR so he can play lesser users (and as you could see decreased in leagues progressively, becoming gold, and then bronze later, which suggest he left league and then got placed again).
And the reason why he does AFK 5’ instead of leaving right away, IMO could be that this way the other users could not take control over his units, and that making sure that his resources wouldn’t be shared with them. So some sort of method to ensure the game is a defeat, and that his MMR indeed lowers.
And I who thought I had seen it all regarding smurfing… 
So after your, I must say thorough investigation concluded there is no botting involved? Just some smurf leaving games after 5 minutes? Well damn. The guy must never sleep then
I mean, I went to bed and he still at it for at least 21 hours, as far as the match history is able to go back
I think he’s there at some moments at least. I am not sure he hasn’t a sort of timer to close the game (which doesn’t necessarily requires a bot, but could be eased by an external program).
As for not sleeping, he could just alt-tab from SC2 to windows at at the start of each game, as suggest the slight camera moves. So he could be watching Twitch, reading at his emails, literally anything and then just closing SC2 process around 5 minutes. 
Hmm. That’s disturbing. Looking back at what I saw, he left most games at nearly the same time as well, at about 5 minerals each time. This is smurfing, and he sometimes does some inputs by himself… but that could be him just watching at how things are going from time to time, and doesn’t rules out some parts being automated.
To make sure, I took a look at the post-game debriefing you first linked (the one of 11:50 Old Estate), which is a different one from my Fortitude one, and the amount of resources mined was 1747… for 1747 in Fortitude, and 1742 in my 26:52 Old estate.
So this is too close to be done manually for 21H long. There might be automated parts to this 4v4 smurfing after all… 
I realized the thread had become quite long, and that this probably discouraged the read. Thus the objective was to make the first post easier to navigate, to allow users to read only the parts they are interested in.
Is data for NA only?
i have a question myself, what level smurfs the most? diamond master platinum ect?
I started the surveys as purely observational ones, by just reporting those I faced as a player. And so it started at EU’s P1-D3 MMR, and I choose to keep on that region for my randomized studies, for them to be as comparable as possible between them.
So all this data is EU. As the question didn’t seem to get people enthused, NA is missing (though as zone changing is an easy way to get an alt, I expect it not to be that different, personally) ; and I didn’t survey diamond and masters leagues either. 
Thanks for your appreciation, Dallarian. 
That’s quite the tough question, PeekaChi ! A lot of smurfs do conceal their original league. 
However, if by smurfs we refer at players playing under their true level, there are some who do that on their main account, or who do ladder climbs from bronze to their original level.
So, for those if we take the example of the bronze league :
BRONZE SMURFS
24 smurfs over 105 players = 28.6% of smurfs
Among those smurfs :
- 12,5% of silver players.
- 20,9% of gold players.
- 4,2% of platinum players.
- 33,3% of diamond players.
- 4,2% of masters.
- 25% can’t tell.
So there are smurfs from nearly all leagues, but this suggests a majority of those smurfing in bronze are diamond players. That’s interesting because that’s also the feeling that I had around P1/D3 MMR. It could be informative to take a look at the other leagues surveys though, because I recall there were a lot of golds smurfing in silver.
it would make sense considering diamond players think they are “”"“good”""" and also are way bigger in population than master league.
I don’t understand the point of smurfing in this game… the whole reason it’s fun is pushing boundaries, and trying to increase your skill. It’s not like League of Legends, where playing amongst weaker players is at least fun.
If someone plays rankeds only in current season and has 75 wins, no loses (100% win-ratio), on a way Bronze 2—> Platinum 2, is that smurf?
I guess it falls into:
often abnormally high winrates as well.
Being « good » is something very relative in this game, as there is always someone better or worse than you. Which is why most players reaching an acceptable skill in most of the game’s domains prefer to say they’re « decent » rather than good.
I think it’s partly because of that because there are so many smurfs from diamond, because they don’t feel that good (due to the matchmaking eventually placing them at a MMR where they have 50% defeats), while they start wondering if they have reached their skill ceiling. And from there, instead of trying to overcome a glass ceiling they’re unsure/unwilling to invest themselves into, some of they turn towards smurfing instead.
It’s also a league where they can more easily get convinced that their limits are related to balance. Which gives people freelosing only specific match-ups.
I think those two events can happen similarly often in diamond and masters, but as there are much more diamonds than masters, in the end this implies more diamond smurfs. 
I think that’s indeed why most of us do play SC2, as it’s one of the most difficult/competitive games of the e-sports scene, and so it wouldn’t make sense to try oneself at it if disliking challenge.
But the amount of challenge a player is ready to accept varies wildly among individuals. And so if they reach a point where they are convinced the challenge is unfair (due to balance… but also to higher leagues smurfs, or even to the matchmaking range), some players choose to forsake challenge and seek fun only.
Some also need victories in order to feel good, or can’t stand defeat anymore (which is a form of increase in ladder anxiety) and so they freelose in order to avoid defeats as much as possible.
I’ve found quantities of reasons behind that behavior ; most of them being rather bad. I’ve noted them all somewhere, in case if the devs would wish to understand the motivations better.
It’s either a walk in the park type described above (the ones who can’t stand defeat), or someone doing Bronze to Masters tutorials. The latter are extremely rare (about 1% of smurfs at most), so chances are that you found a bad one. 
Nevertheless, your target indeed fulfills the criteria for a non freelosing smurf. You’ve successfully hunted your first smurf, Dallarian ! ^^
So I took a closer look at your smurf. Quite an interesting specimen indeed. Here’s a sample of some of his accounts :
On top is the one you’ve met, with a zerg account. He meets two criteria for non freelosing smurfs, with :
You’ll note that he started at an extremely low MMR (1728 which is bronze 2), so he must’ve freelost some games, but those aren’t registered into his league winrate. He also has 245 games career. So my guess is that he freelost some games, in this season and possibly the previous one, and then left league in order for those not to be registered.
The second one is his terran account. Way less spectacular than his zerg one, with only 53% winrate upon reaching platinum MMR. Though there might be some freeloses among those, I can’t be sure. There probably were when he went from mid gold to mid silver MMR.
Last is one of the oldest account. As you’ll have noticed, the historic starts in gold with about 60% winrate. This suggest even this account isn’t his main one. He still has a positive W/L difference upon reaching diamond 3, which suggest his true level might be one tier or two above this one.
It’s worthy to mention that those 3 accounts are fully independent from each other, so one isn’t the offrace of the other. However, they have the exact same capitalization for the pseudo, and do share the same portrait for two of them, the last one being a typical smurf’s default avatar.
From his forum activity, we could gather a considerable amount of whine threads regarding terrans and protoss races, which I won’t quote for him not to be recognizable, but among those we have things like Zerg is unenjoyable ; when will zerg have cool and viable units ; had enough as a Zerg in ZvT ; Z can’t keep up with protoss economy, on and on…
If we sum-up :
So what we could think is that for this individual, having fun = having victories, and that starting around 2016 he charged his decreasing fun/victories over a balance perceived as unfavorable. The fact he has two zerg smurf accounts, and that one of those is much older than the two others accounts IMO indicates that he smurfed in order to find back his winrate (= fun to him) rather than to seek new challenges.
To summarize : a perceived imbalance and a notion of fun associated more with victories than challenge. Interesting case.
I got a few of those points myself (also checked similar accounts), but your wider explanations are simply great.
How do you track and distinguish accounts from other players? For example there are 165 data entrys for GhostDragon, but that includes many servers, races and gamemodes. The phrase could appear in mind of few players (SC is pretty popular after all ^^) so there could be a few different people with exacly same nick.
Also I see you have not tracked his original nick. He changed it around time when he became a barcode, however there are ways of recovering it (I am proud to succeed before you 
). There are 120 data entries for this and similar nicks, but as I said, it could be multiple players.
Is there a way of filtering such results? One of them is M3 since June 2020 (rankeds played since April 2020 on lvl of D3), with a result of 15/7, but well, it could be a different person, or he uses many nicks.
I mean, I don’t suspect people to be desperate enough to create 30-50 same nick accounts (and unique emails for each!) and play them on different servers with different races to generate 150 data points, but I still know little on smurfers. Such thought genuinly can’t appear in my mind.
Well you can’t, that’s the whole point of smurfing.
Jokes aside, there are small clues that might help. In that case it was the distinct capitalization of his name. Aside than that, general smurfing indications (low amount of career games, default avatars, MMR big fluctuations, winrates etc. etc.).
It would be hard to tell. There are minor clues that might be exploitable :
Some of those require to have met him ingame, which is quite limitating ; but can be quite efficient nonetheless. Heromarine recently identified on stream one of Lambo’s smurf with the builds and control groups. It was quite the interesting investigation work. 
For the sake of demonstration, he mentioned having played zerg since around 2010, so you can eliminate all the accounts < 2016 as not being the main ones. As for knowing his previous nick, that’s an advantage you indeed have ; but it’s more reliable to have the profile sheet (with the numbers), as the battletag can be changed.
It’s highly improbable he has that many accounts. But 3, 5, 10 ? Not impossible. He has several smurfs aside of his main one, that’s the only thing we know for sure.
