There are four potential first-round picks in the college shortstop ranks for the 2009 draft, and all are prominently on display this summer. Miami’s Ryan Jackson is slated to be the everyday shortstop for Team USA, while Southern California’s Grant Green (Chatham), Louisiana State’s D.J. LeMahieu (Harwich) and Division II Florida Southern’s Robbie Shields (Cotuit) are playing in the Cape Cod League.

Green and Shields have both gotten off to impressive starts in the Cape, and highlight this week’s Summer 10 ranking—a list of 10 college players performing to a high standard this summer in the nation’s summer college leagues. We’ll occasionally include players from Team USA, which dominated last week’s ranking with five of the 10 spots, but we’ve elected to focus only on players in true summer-league competition with this edition of the Summer 10.

Chatham’s Green, projected to be the first college shortstop drafted next year, was hitting .421-1-6 through his first 15 Cape League games, and also was tied for the league lead with 24 hits. In the field, though, Green had committed a league-high eight errors. Shields, meanwhile, has impressed scouts with his solid all-around play. Not only has he hit .349-2-11 for Cotuit and been a key component in the league’s best offensive attack, but he has been flawless in the field, committing no errors in 11 games.

LeMahieu, who played a key role as a freshman in leading resurgent Louisiana State to a berth in the College World Series, got a late start to his summer season and had just joined Harwich. He is draft-eligible as a sophomore.

Based primarily on on-field performance to date, here’s this week’s Summer 10: