Who Should Start Game Four for the Phillies?

Philadelphia Phillies skipper Charlie Manuel is expected to decide soon that Roy Oswalt will be the fourth starter for the club heading into the postseason. The decision obviously would come at the expense of 23-year-old standout Vance Worley, whose rookie season has made some folks in the City of Brotherly Love wonder if he’s the real fourth ace in this star-laden rotation.

Certainly, Manuel’s decision would have been expected in April when the Phillies entered the season with Roy Halladay, Cliff Lee, Cole Hamels and Oswalt on staff; but a flurry of ineffective starts — and two trips to the disabled list — have marred Oswalt’s season. Worley, meanwhile, now looks like the guy who should have been manning that fourth spot all along. His ERA is 3.00 — compared with Oswalt’s 3.66 — and Worley’s defense-neutral estimators all are about a third of a run better than Oswalt’s, as well.

So should Oswalt really be such a lock for that start? Well, here’s the way to tell: Tell both pitchers to warm up, and then put the radar gun on the 34-year-old’s fastball. If it’s above 91.5 mph, put in Oswalt. If it’s below — well, you know the answer.

Below is FanGraphs’ plot of velocity by start for Oswalt. Note that these charts don’t include his Sept. 12 start (91.87mph) and his Sept. 17 (91.85mph), which are a small decrease from the last start pictured, on Sept. 7 (92.18mph).

Notice that I’ve drawn a thick red line down the center at 91.5 mph, dividing his starts into games when he had his fastball velocity working and games when he didn’t. This red line represents the difference in between the fourth ace that the Phillies thought that they had all along and the below-average pitcher who has been bested by a bespectacled rookie. The ace Oswalt gives up half as many runs and strikes out 50% more hitters — while the other Oswalt has a strikeout rate that would rest somewhere between Livan Hernandez and John Lannan on the National League’s K% leaderboards.

Velocity	GS	IP	ERA	SIERA
91.59-93.04	8	52	2.25	3.32
89.85-91.44	13	73.1	4.66	4.29

While ERA can be a useful tool to evaluate pitchers, it struggles when dealing with small sample sizes. Because of that, I dug deeper to confirm my suspicions. I broke down Oswalt’s performance into buckets — shown above by thinner black lines on opposite sides of the thick red line, representing at 92 mph and 91 mph — to see how his peripherals and his SIERA moved with his velocity. In fact, Oswalt’s SIERA is more than run lower when he’s at his best, thanks to a strikeout rate almost double that of his inferior alter ego.

Velocity	GS	IP	ERA	SIERA	K%	BB%	GB%
Over 92.0mph	4	27	1.67	3.26	22.0%	7.3%	52.7%
91.5-92.0mph	4	25	2.88	3.40	17.3%	3.9%	49.3%
91.0-91.5mph	6	29.1	5.22	4.31	12.7%	5.2%	39.6%
Under 91.0mph	7	44	4.30	4.29	13.4%	5.7%	41.3%

Deciding between Oswalt and Worley isn’t really that hard because Manuel doesn’t have to choose between two similarly competent pitchers. Rather, he’d be choosing among two of three possible pitchers who show up in the bullpen: Worley, Good Oswalt or Bad Oswalt. Fortunately for the Phillies, the difference between Good Oswalt and Bad Oswalt is easy to root out. Charlie Manuel just needs to bring his radar gun.