Doug Fister has thrown almost exclusively fastballs in his last two starts and because of that, and a few other occurrences such as Brandon League neglecting his splitter, people have begun to ponder about the increased use of the fastball in 2010 possibly being a staff priority. Granted it is still early in the season, but I felt it worthy of further investigation.
Question 1: Is the team as a whole throwing more fastballs?
According to FanGraphs, the Mariners pitching staff as a unit have thrown a fastball 66.1% of the time, the third highest percentage in the league behind the Tigers and Indians. That's a lot of fastballs. However, in 2009, the Mariners actually led the league in fastball percentage at 66.8%, higher than it currently is. So no, while the team does throw many fastballs, they are actually throwing them less often this season than they did in 2009.
Question 2: Why do they throw so many fastballs?
Is the high percentage of fastballs a product of Rick Adair's philosophy (the fastball % was more pedestrian pre-2009) or a product of the pitchers making up the pitching staff now? I'm trying to find out from the principals involved but there no way to determine the answer simply by looking at the data and any reason I offered in the meantime would be perilously subjective.
Question 3: Who's throwing the fastballs?
The bullpen is. At 75.1% fastballs, the Mariners' bullpen leads the league by a wide margin. The Indians' pen is second at 71.4% and the Rangers and Tigers are tied for third at 68%. This is not new; the Mariners bullpen led the league in fastball percentage last season as well, at 73.4%. This does not come as a big bombshell given the makeup of the bullpen. GM Jack Zduriencik went out and crammed the pen with hard throwers; the average fastball thrown by Mariner relievers also ranks near the top of the league.
Mariner starters rank around 10th in the league in fastball frequency. They are actually second in the league in changeup frequency.
Question 4: Is it harming the team?
Should the Mariners be throwing more changeups and fewer fastballs? This is a difficult question to answer. We would need a complex game theory matrix to fully judge and it would be so bogged down in small samples that it would be difficult to get a precise measurement. A rough estimate would suggest that the Mariners would be better off with a higher number of changeups from their starters and more breaking pitches from their relievers, but whether that should come at the expense of fastballs is nigh impossible to say with confidence.
Nevertheless, I can point out that the fastballs thrown by the Mariners pitchers rank fourth best in the league according to FanGraphs' pitch values and they were fifth best last season. The Mariners may be throwing a lot of fastballs but at least they're good fastballs.
The short answer is no. I looked at all the pitches caught by the two catchers from the various starters and after controlling for the pitcher, neither backstop shows a significant difference. Adam Moore has caught 96% as many fastballs as you would expect given 2009 frequencies while Rob Johnson is at 97%. I have no basis to make this claim, but that their fastball (and other pitch) frequencies are so similar prompts one to wonder if most of the pitches are being called from the dugout and not from behind the plate.