There are two aspects to measuring defense: fielding percentage, and plus/minus.
Looking at the second, plus/minus - you are fine, at 12/1.
Looking at fielding percentage, i.e. errors, we can see who's committing the most errors:
- Knight - 5 errors at SS - glove is slightly below recs, but only by 2 points - he should be OK, chalk this up to SSS
- Sexton - 4 errors at LF - glove is six points below the recs - he's going to hurt you defensively in LF - you might want to move him to 1B and move Johnson to LF
- Merrick - 3 errors at 3B - he's above all the recs for the position, chalk this up to SSS
- Hunt - 3 errors at 2B - he's above the recs for the position except for slightly below in range, but that doesn't manifest itself as errors - again, SSS
Overall, I'd swap your LF and 1B and just ride it out. Most of the problem just seems to be a stretch of bad luck defensively.