The manager is played by Russ Brown, and the three ball players from left to right are: Albert Linville, Nathaniel Frey and Jimmy Komack. All four, by the way, were in the original Broadway production.
The latter two are the most notable. Komack later -- as James Komack -- became an extremely successful TV writer and producer, most notably as executive producer (and a somewhat controversial one) of Welcome Back, Kotter. And Nathaniel Frey, with an extremely distinctive deep New York voice, is one of my favorite Broadway character actors, often used by Harnick and Bock -- co-starring in their Fiorello! and She Loves Me.