Or more specifically, should the Mets trade him for Nick Johnson, the rumored Nationals' asking price? James got me thinking about this question, and there's a pretty interesting debate to be had. Usually, I don't give full consideration to ever rumor that's whispered, but usually I have an immediate yes-or-no reaction. On first impression, I think I know what most would say. Mets fans are enamored with Parnell, and rightfully so, he's pitched well. But are we overrating him? Without considering the potential impacts on the rest of the bullpen, consider what kind of player Parnell is in the abstract.
He is not dominant. I know it's trite, but consider this Player A, Player B comparison:
Player A: 18.75% K, 10.16% BB, 60.7% GB, 11.2% LD
Player B: 18.10% K, 9.48% BB, 36.1% GB, 19.3% LD
Pretty similar, eh? On first glance, Player A seems slightly better. Well, if you don't know or haven't cheated, Player A is Sean Green and mystery man B is Parnell. The difference between the two, and their ERAs, is homers allowed. Given Parnell's relative flyball tendencies relative to Green, however, one would guess Parnell will have the worse luck going forward. Disregarding the youth and the 95 MPH fastball, Parnell seems like just a middle reliever. Not a closer-in-the-making, but a good, not great, piece in the bullpen.
Considering the youth and velocity, however, should we expect Parnell to improve? Without a credible secondary offering, the velocity of the fastball means less. His slider is more of a show me pitch, not an out-pitch, evidenced by his extremely low number of swinging strikes. This reliance on the fastball also makes it unlikely that his efficiency and walks improve, as he's got to locate his fastball and hitters can just sit on it and foul it away.
On the flipside, one could argue Parnell is necessary to preserve the stability of the bullpen. With Putz out and Stokes looking ineffective lately, the innings before Francisco Rodriguez need dependable relievers. Still, I think this argument gets blown out of proportion because of Mets fans' sensitivity to late-inning meltdowns. This bullpen, however, does not feature Aaron Sele or Guillermo Mota. Green, Feliciano, and Stokes could all probably do the same job. Wagner also says he'll be back in 30 days.
Other arguments for Parnell are that he's gotten unlucky with balls in play (.378 BABIP) and has been a better groundball pitcher historically (53.5% GB in the minors). Still, a fastball-first pitcher will see his share of homers, and they Mets could be said to be selling high for that reason.
If you can make the leap of faith that the bullpen will hold up, the swap of Parnell for Johnson in terms of straight value seems to favor the Mets. Parnell, in his current state, is worth about a win per season. That's probably his upside too, as he's unlikely to improve much from how he's pitched so far, and middle relievers rarely are worth more than a win. I wrote about Johnson earlier:
Assuming 300 PA and each firstbaseman playing to expectation, Johnson could be roughly a 2 win improvement over Delgado.
That figures to at least a 1.5 Win improvement, with a competent AAA reliever, or the return of Wagner, completely mitigating the loss of Parnell. Considering how Murphy's playing lately, the benefit may be even greater. Johnson would be a definite stabilizing force in the lineup and a great option to resign after this year. If you had told me before the season we could swap Parnell and some other worthless "prospect" like Kunz or Stoner for Nick Johnson, I probably would have done it, with Delgado healthy. Given the Mets situation now, however, the move seems like a no-brainer. The Mets would be wise to sell-high, and get a long-term solution at first for a middle reliever.