Jeremy Guthrie, Duchscherer (if healthy) and Brian Matusz are locks for the rotation. Bergesen is probably staying...he's not great but fairly reliable. So Tillman and Arrieta are dueling for one spot.
Some point to Arrieta's September as proof that he has turned a corner and should be the front runner for the final spot in the rotation. But while the numbers are great (2-1, 2.60 ERA, 13 K, 2 BB) but it was only over 17 innings. But over the course of the season, he walked nearly as many as he struck out. Not a good recipe for a young pitcher to make a leap forward.
Speaking of the numbers...
IP K BB HR ERA FIP WHIP Arrieta 100.1 52 48 9 4.66 4.76 1.535 Tillman 53.2 31 31 9 5.87 5.89 1.528
Yeah...still doesn't look great for Tillman here.
But it seems to me that Tillman got more "swings and misses" with his stuff last season. So let's compare with the data from Fangraphs. O-Swing is swings outside the strike zone, Z-Swing is swings in the strike zone. Swing is total swing percentage, F-Strike is first pitch strikes and SWStr is swinging strikes.
O-Swing% Z-Swing% Swing% F-Strike% SwStr% Tillman 25.2% 66.0% 43.2% 50.0% 6.3% Arrieta 29.0% 61.6% 43.6% 54.1% 5.7%
I thought Tillman would have had a bit more of an advantage here but they are pretty much even. Which is disappointing. I would have expected a bit more swinging strikes from Tillman's stuff than Arrieta's but up to this point, they are in a dead heat.
If I had to choose, I still like Tillman's upside better than Arrieta's but they are very similar at this point. This spring, I'd watch the strikeouts and walks for both of these guys very carefully. Homers will happen in Florida, ERAs and Wins will fluctuate with the defense but the walks and strikeouts will be the best bellwether for their competition in Sarasota. And it starts tomorrow when Tillman takes the mound against the Phillies.