The Mets have called up outfielder Michael Conforto, their near-unanimous top prospect on our midseason list and one of the better-rated Mets prospects on some national lists this year. Between High-A St. Lucie and Double-A Binghamton this year, the 2014 first-round pick has hit .297/.372/.482. He hit .312/.396/.503 in 197 plate appearances with Binghamton after he was promoted there earlier this year.
Expecting Conforto to replicate that line in the majors wouldn't be fair. But there are several projection system for baseball performance out there, three of which have forecasts for Conforto in the big leagues.
For context, major league left fielders have hit .255/.319/.402 this year. If Conforto were to hit like the projections predict, that would pretty much make him league average at the position. While Michael Cuddyer has disappointed with his .240/.303/.380 line this year, expecting Conforto to be vastly better than that would probably be unfair. But league average production at the position would be a perfectly acceptable outcome for a player making his major league debut.