Last week Nats fans were ready to declare Detwiler the third starter for the playoffs. Then Edwin Jackson came out and pitched 8 innings of 1 run ball and made the situation confusing again.
The 3rd starter role is going to come down to alot of things. How much does Davey want to alternate righties and lefties? What's the tendencies of the team you are facing? Are the Nats truly going to a 4 man rotation or are they going to try to role with 3 so Gio or ZNN could potentially pitch 3 times? Even if we could answer these what it could comes down to is who pitched better in their last start, and there's no way we can know that now. We'll take a look at recent stats though and try to get a feel.
Davey and L/R alternation
Davey's L/R tendencies aren't clear. He's only pitched back to back lefties a couple of times before Strasburg was shut down, and since then only back to back righties once, when Wang took over for Lannan and it was unavoidable. So it seems he favors alternating. Then again all he really did was set the rotation up as anyone would. Strasburg, Gio, ZNN, Jackson, Detwiler? That's how I would have ordered the rotation by talent to start. The alternation is just a happy side effect.
Looking at his other teams doesn't help clear things up. His Dodgers teams tended to be overly righty making a judgement impossible. His Orioles teams showed no strong inclination to split up righties and lefites, going RRRLL for a fair amount of the 2nd half of 1997. His Reds teams were a mess of injuries but in general I'd say he favored alternation there.
The Giants and Reds show a slight preference to facing lefties, but it's not strong enough that I'd base any starter decision on it. The Braves struggle against lefties, Bourn, Heyward, McCann, Freeman are all lefty batters and Chipper hits noticeably better from that side. The Cardinals are very strong against lefties. Craig, Molina, Freese, Holliday all bat from the right side and Beltran shows way more power there.
4 man rotation or not?
No idea. Davey has often gone 3-man. He did it with Darling, Schourek, Mussina, Erickson, Wells. Young and old, when he had decent 4th pitchers, and when he didn't have necessarily a good #1. It's actually been something he's been pretty consistent about and deserves a deeper look into in another column. It was different times though. Guys are protected more. I'd be shocked if ZNN pitched on 4 days rest. He hasn't gone over 7 innings or 108 pitches this year. Gio... maybe. Old Davey would have probably set something up like Gio, ZNN, Jackson, Gio, Detwiler, ZNN, Gio. New Davey?
2nd Half : ERA 3.81, WHIP 1.23, K/9 9.63, HR 11, BABIP .310
Last 6 : ERA 4.06, WHIP 1.19, K/9 9.80, HR 3, BABIP .340
Last 3 : ERA 5.00, WHIP 1.22, K/9 7.50, HR 3, BABIP .308
2nd Half : ERA 2.76, WHIP 1.07, K/9 5.06, HR 5, BABIP .251
Last 6 : ERA 2.57, WHIP 1.20, K/9 6.17, HR 3, BABIP .274
Last 3 : ERA 2.65, WHIP 1.29, K/9 6.88, HR 3, BABIP .269
While the ERA gap screams start Detwiler, everything else, especially more recently, is not as clear. Detwiler is going to have a lower BABIP than Edwin. He's a GB pitcher on a team with great IF defense. But that much better, suggests a bit of luck (either bad for EJax or good for Det, or both). Detwiler's Ks are moving in the right direction but he's also getting hit/walking more. Edwin's K's are heading down (but are still better than Det's) while his WHIP is stable. Edwin's last 3 include his last bad game. He looks better in the last 2 obviously. I'd say Detwiler has the edge here but not by as much as you think
Other things to consider
Edwin's last start really highlights something he can do that no one else is allowed to. He will pitch deep into games. Whereas Detwiler has an unofficial 7 inning 100 pitch limit (hit 7IP 5 times, 100 IP once, never past), Edwin has no such limits. He's gone over 100 pitches 13 times and he has 6 7IP games... and 4 8IP games... and one complete game. Edwin is a veteran arm on a one year deal. Stretching him out makes much more sense than risking Detwiler, young and in control for a few more cheap years. If the pen needs that long game, there's no question you try to go with Edwin.
Dewilter has also worked the pen this year and was really good in his limited time (~13 IP - which by the way is why his ERA is lower than Strasburg's. He has a 3.26 starter ERA. YOU CAN'T JUST IGNORE THIS PEOPLE)
My guess, barring a flame out by either, is that the tendencies are going to drive the decision in the NLDS. If the Braves are the team, then Detwiler gets the nod. If it's the Cards then you'll see Jackson. The differences in their pitching right now aren't big enough not to try to play away from the other team's strength. If the Nats get there, in the NLCS and WS, I think we'll see whoever's hot. If there is no clear "hottest" then I give the nod to Jackson, based on his ability to go deep and Detwiler's success in the pen. In either case, I'm also thinking that we will see Gio pull a 3 dyas rest thing if necessary, maybe a couple times.