[rburgh]

1. You play in a very low-run environment ballpark.
2. Your closer needs to be upgraded.
3. You need to be more aggressive with pinch hitters in the late innings.
4. You need to stop bunting and hitting and running, those are small ball strategies.
5. Your team is just at a higher level than your talent warrants.
6. You need to get your starters out of the game earlier. Experiment with giving them pitch or batter limits on the player strategy page. Or you can just put a pitch limit in the box beside his stamina rating when you look at your starting rotation overview on the pitching management page.

I'm sure other users will have more possible solutions.