There's more to being a major-league pitcher than throwing hard. Plenty of pitchers have had successful careers without making the mitt pop. On the whole, though, throwing hard helps. All else being equal, the harder a pitcher can throw, the more effective his offerings are and the easier it is for him to get away with mistakes. It's no coincidence that the team with the hardest-throwing staff this season, the Washington Nationals, also boasts the big leagues' best ERA.
In a 2010 study, PITCHf/x analyst Mike Fast found that starting pitchers from 2002-2009 allowed, on average, 0.28 fewer runs per game for every mile per hour of velocity gained. Relievers, who tend to rely more heavily on their heaters, allowed 0.45 fewer runs per game for every extra tick.
So far this season, pitchers who've seen significant declines in velocity have suffered even more dramatic declines in performance. The average four-seam fastball velocities of 27 starters have fallen by at least one mile per hour from 2011 to 2012. Despite a league-wide decrease in scoring, those starters have seen their combined ERAs rise from 3.59 to 4.31, an increase of 0.72 runs.
The five starters whose four-seamers have slowed by at least two miles per hour -- Alex Cobb, Graham Godfrey, Tim Lincecum, Justin Masterson and Carl Pavano -- have had even more disastrous results: Their ERAs as a group have inflated from 3.44 to 5.55. These figures aren't park-corrected. We're comparing full-season velocities from 2011 to partial-season velocities from 2012, and fastball speed tends to increase as the season goes on, but those declines are still scary.
However, a handful of pitchers whose fastball velocities have declined by a mile per hour or more since we last saw them have held their own or made real improvements in performance in 2012. Here's how they've done the job despite diminished stuff.
Four-seam velocity: 89.1 (2012), 90.2 (2010)
Difference: minus-1.1 mph
Santana's season qualified as a success the moment he stepped onto a major-league mound, something he didn't do as he spent last year recovering from September 2010 shoulder surgery. However, not only has he been healthy, he's been a better pitcher than the one the Mets saw before the injury, recording the fifth-lowest ERA among NL starters and pitching the first no-hitter in franchise history.