Please xplain how these player ratings can change like this

I'm not trying to pick on Janek.  He was my opponent yesterday and I looked at his stats iand I don't understand them.  As you can see he has only had 7 recent games.  He was rated 1317 on Sep 2, and didn't play again until Sep 23 where he was rated 1438. On Sep 2, he beat a player almost 300 rating points below him.  I would expect that would increase his rating by maybe 3 points, not 121! 

The other strange jumps in rating are there to see.  I must not understand how the system works, but looking at my stats, my ratings usually change from 5 to 11 points depending on the strength of my opponent.  Is there a logical explanation?  

Google Glicko RD

blueemu is right. Basically, this player (Janek_999) has a relatively new chess.com account with few chess games played. When the rating algorithm calculates the change (upon game result), the algorithm factors in the fact that this player may not yet have an accurate rating yet; basically, the rating will swing around a lot before it settles. Our games give up maybe around +8 points for a win since there are more games recorded (I think the variable is the "k factor", but it ajusts as more games are played).

Imagine no rating system exists: how accurate could you guess a rating? Let's say that little Bobby plays his first rated chess game and beats an 1800 player. Is Bobby rated around 1800? No, of course not: little Bobby just got lucky as his opponent blundered; Bobby might only be at a true rating of a 1000 player. Now what if after the single game I mentioned that "little Bobby" is actually "Bobby Fischer": that game was no fluke and the "true rating" will rise soon.

Why does the algorithm allow such crazy swings in the first place? It is an attempt to quicker assess "true rating". If it did not do this, then Bobby Fischer caliber players would need to win rating only 8 points at a time and take away rating from every opponent along the way. Not all rating systems do this, but it helps quicker get them to the correct ratings while also preserving ratings of opponents played against.

Indeed. I recently played a newcomer whose initial rating was 1800. But I pried alittle bit into their stats just to get a "feel" of their game and noticed that they hadn't played any games! I was the first. Anyways, I did lose the game and noticed their rating shot up to 2001. Apparently this player had won another game with an opponent with a similar rating. This was in daily chess format of 1 day. I guess they were strong looking at the other stats: 1900s in bullet & rapid play. On a side note though, while I lost 15 points in that game, I noticed my rating had not changed in play with my other games. Or say, in one day I lost 15 but the next day it was given back to me! Strange but it's cool. Like the previous poster said, maybe it's provisional until enough games have been played until it's settled on a more concrete rating.

lots of those dudes start an account to go on a win streak; if they lose, they dump it and start anew; yeah; i don't even.