Home run rate drives the difference between Perez and Griffin in terms of FIP, while BABIP and LOB% dirve the ERA difference. K% and BB% are similar for both. Perez needs help from his D, while Griffin doesn't let his D help when balls are out of the park. Griffin has been hit around a lot his last two outings (14 ER over 9.1 IP). Perez has had only one rough start: his last one, when he gave up 4 runs over 5 IP but limited damage with an unusual 10Ks.
White, Kim, and Sandy Leon are in the lineup, with Acuna DH'ng. Nats go with their lineup against lefties, with Mead, Chappy, Young, Nunez, and Ruiz playing. It's not a straight every-other-day alternation of Ruiz and Millas; Millas doesn't start against lefties. Lile is the corner OF that gets to DH, while Wood shifts to left.