Player Attribute increases

[splodem]

I'm doing a season with a buddy of mine, and have noticed a few of my players like David Wright have stat increases, like +1 to HR vs Lefty, and whatnot. My pitchers have a few point increases as well. Their overalls are still the same, and the increases are listed as green numbers. Do these become permanent increases over time? Somehow Derrek Lee gained +1 to HR vs Rigthies, and after a day or two it dissapeared, but his overall is now up to a 89, but nobody else has increased yet. How does this all work? Any info is greatly appreciated!

[omgzjasonlol]

It's related to how well or poorly they're playing as well as their happiness with the team. You can check all of this at the Team Buzz screen under the GM tab.