There is no such position in baseball. The running back position is used in American football.
This position is called short stop.
Shortstop
1
the line
The "keystone" in baseball usually refers to second base. It's called such because it is important in scoring (since a runner on second is in "scoring position") and because it's a key defensive position.
Pitcher
Position
YES
Right field.
Catcher
The position abused by steroids in base ball are batter, and thrower.