A common question for fantasy baseball players to ask at this time of year is "Is it time to worry yet?". The correct answer is "it depends". Some situations where poor performance might be reason to worry:
1. There are concerns that an injury is contributing to the player's poor performance.
2. The player is in danger of losing playing time due to the poor performance.
3. The player is old enough that the poor performance may indicate that they've reached the steep part of the aging curve.
4. A pitcher has poor peripheral stats (K/9 and BB/9) AND is showing reduced velocity on their fastball.
If none of those conditions are present, then it's much too early to worry. On one popular baseball forum, a number of people said that they were worried about Hunter Pence. Why? This is a player who has a fairly established performance level. He just turned 27 years old. As far as a I know, there are no injury concerns and there's no risk of him losing playing time. If you're playing in a league where he may be available at a discount, he's exactly the type of player you should be targeting.