Lost 30 rating points for no reason

You drew against a lower rated player, so it is expected you would lose rating. At first look, it seems a little high for a draw and your RD, but without going through the calculations, I can't verify that, but it probably is accurate.

Lets look at the games before and after the draw.

Before that game he beat someone rated 98 points higher than him. "Normally" that's wroth 12.6 points. He gained 10. That's a multiplier due to the RD of 0.79

Then he drew someone rated 64 points lower than him. "Normally" that would be -1.8
It was -28, so his multiplier was 15.56

Next game he beat someone 116 points higher. That's normally worth 13.2 points. He gained 11 points. A multiplier of 0.83

So the games before and after have a multiplier below 1, which is normal IMO for an RD around or below 20.

But the multiplier for his drawn game was ridiculous. I know topics like this are usually easily dismissed because the user is technologically, mathematically, and socially illiterate. But this time I'm not sure why he lost so many points. Looks like a legitimate question.

It could be wrong. Opening a ticket to support would be the best way to verify.

https://support.chess.com/article/346-contact-us

(edited post for correction on numbers, still same conclusion though)

Maybe I misunderstand chess.com's system. It seems his multiplier was higher for his later game... maybe we could say that's based on that opponent having a lower RD (and so opponents with more established ratings hit you for more points)... but that still doesn't explain losing so many for the drawn game.

Although... since I'm merely estimating (plus or minus about 0.8 points) what he "should" be gaining or losing, maybe that explains the multiplier difference for the 1st and 3rd games. That leaves the 2nd game (the draw) with the inexplicable rating.

Yeah, looking around, the loss probably should have been closer to 8 points. Their RD values are both pretty low and the ratings were within 100 points.

Ok, I typed up a nicely formatted report. I'll try sending it off.

Hey, I'm drunk, I log in to burn time, I might as well do that.

Plus it's fun because most people have no idea how ratings work.