Pinch runner

My lf got injured and I needed a pr. Why would Hal pr one lf and then put another in lf when they have the exact fielding rating and br ratings? Just to waste a player and how to avoid this?

Just a guess, but do you have the first guy designated as your PR and the other guy designated as your defensive replacement for LF on the strategy page? Or maybe the PR is marked to be removed for a defensive replacement on the hitter's preferences? If neither, then you got me.