Kevin Kennedy thinks Jonathan Broxton's pitching problems last season could be attributed to mental issues rather than anything physical. Here's a comparison of his last two seasons:
Broxton's fastball lost more than two miles per hour of velocity in 2010, and his slider lost more than one mile per hour. Perhaps a mental component played a part, but when a pitcher loses a significant amount of velocity on his two main pitches in one season, it points more towards a physical problem more than anything else.
Broxton's slider had the worst dropoff between his two pitches, with opponents wOBA increasing .181 versus it last year. Opponents were also making much better contact on the pitch, and his k-rate dropped a bunch. A higher BABIP might suggest he was somewhat less lucky with his slider in 2010. However, in 2009 he yielded all of two fly balls on the pitch, and no HRs. But the following year, 25% of the balls in play off his slider were fly balls, two for round trippers. With opponents' averages increasing fairly equally on line drives and ground balls against Broxton's slider, I'm more inclined to believe they were squaring up the pitch better last season, rather than just getting lucky with hit ball location.
Broxton was also leaving his slider over the heart of the zone more last season, especially against RHB who accounted for much of the damage.
The small increase in sliders hitting the center of the plate accounted for a good deal of the overall damage down by RHB. They produced an .800 slugging percentage on sliders over the middle of the plate last season, compared to a .231 SLG% when they ended up hitting the outer 3.5 inches of the plate or further.
I wouldn't totally discount that Broxton's problems could partially be a product of mental lapses. But there is enough evidence from pitchFX data alone to suggest that his pitches didn't have the same bite as the year before. Keep an eye on his pitch velocity early in the season. If he's back to 2009 levels, it could be a sign that he's regained his form.