CINCINNATI — Before he would trust the scouting acumen of Clayton Kershaw, Zack Greinke had to test him. Greinke, the National League’s starting pitcher in the All-Star Game on Tuesday, does not need to evaluate amateurs to earn his paycheck from the Los Angeles Dodgers. But he takes his hobby seriously, and even a teammate as accomplished as Kershaw might not have an eye for talent.

“He showed me different left-handed pitchers,” Kershaw said, “and asked what I thought about them — before knowing where they were supposed to be drafted — just to see if my opinion was worth his while. I think I did O.K.”

Scouting the skills at Great American Ball Park will be elementary.

Greinke will throw the first pitch of the game to Mike Trout, the reigning American League most valuable player, and will then face Josh Donaldson and Albert Pujols. His catcher will be Buster Posey, and his bullpen will include Kershaw and a dozen others.