Nats’ post-season roster: The starting rotation

The Nats are in the enviable position of having five good starting pitchers. With extra days off during post-season play, a four-man rotation can pitch with the usual four days of rest between starts, which means that the worst starter gets bumped out of the rotation. Who’s the Nationals’ odd man out?

If we just ranked them by this season’s ERA, it looks like Doug Fister is the ace:

1. Doug Fister, 2.55
2. Jordan Zimmermann, 2.83
3. Tanner Roark, 2.85
4. Stephen Strasburg, 3.34
5. Gio Gonzalez, 3.79

Of course, these decisions shouldn’t be based just on this season’s ERA.

The difference between the stats junkies in the media (I’m looking at you, Thomas Boswell) and the sabermetric researchers is that the media “experts” focus on ever narrower statistics—for example, ERA since the All-Star break, ERA against likely opponents, whereas the sabermetric experts look at a wider set of statistics—multiple years of data, and additional statistics like fielding-independent pitching (FIP) and its relatives (xFIP, SIERA, etc.) I remember Bill James making the point in his Abstracts 30 years ago that you can better predict post-season performance from the players’ statistics for the last two years than from the current season alone. And since then, Voros McCracken taught us that fielding-independent statistics do better at predicting future ERA than does a player’s past ERA.

These factors suggest that the ranking of the Nats’ starters should have Strasburg (3.10 FIP and 2.84 xFIP over 2013–14) and Zimmermann (3.09 FIP and 3.32 xFIP over the same span) on top. Even though Fister’s fielding-independent numbers aren’t as good, with his experience and success at inducing weak contact makes him a natural for the third spot. So the fourth spot comes down to Gonzalez versus Roark.

Gio’s experience and ability to get strikeouts gives him the edge. But I’d also consider the opponent – if the opposing team in a series has hit lefties especially well, I’d be inclined to pick Tanner for that series. Let’s look at the probable playoff teams, 4 teams seem to hit better against lefties than righties:

• Angels (.276/.340/.436 vs LHP) (.257/.321/.402 vs RHP)
• Tigers (.284/.339/.453 vs LHP) (.274/.329/.420 vs RHP)
• Cardinals (.253/.327/.387 vs LHP) (.255/.321/.367 vs RHP)
• Royals (.264/.322/.381 vs LHP) (.259/.307/.371 vs RHP)

The Dodgers, Athletics, Pirates, and Mariners, on the other hand, hit better against right handers, and the Giants and Orioles are pretty much neutral. So I’d consider putting Roark in the rotation should the Nats face the Cardinals, Angels, Tigers, or Royals.

Who should be the Nationals’ ace—the pitcher called on to pitch the most games and to face Kershaw or Wainwright? In my mind, it’s obvious that it should be Strasburg. Even though his average pitching performance may have been a little worse than the other pitchers in our rotation this season, he’s still the guy who gives you the best chance of pitching that shutdown game that you’d like when you’re up against a Kershaw. For example, in 12 of Strasburg’s 32 starts, he’s had a game score of 65 or higher. None of the Nats’ other starters have more than 9 starts with a game score that high.  Strasburg’s ability to get strikeouts and avoid walks simply gives him the best chance for an outstanding performance, even if he does occasionally get blown out.

The other thing to emphasize is that whoever gets sent to the bullpen (probably Roark) has the chance to play a key role in saving games in long relief, as Lincecum demonstrated in the Giant’s 2012 World championship post-season. If a starter gets in trouble early, he’d give us the chance to still come back and win the game.