Red can play this dice roll completely safely by moving 5/3, 5/2 or he can take some risk with either 5/off or 3/off, 2/off.
It should be clear that 3/off, 2/off is much better than 5/off. It takes two checkers off rather than one and it continues to block White’s fives. Both plays give White one bad entering number, either 51 or 21.
Is the risk of 3/off, 2/off worth the reward? Firstly, note that 3/off, 2/off only leaves nine shots because 42 doesn’t hit (it must be played by entering on Red’s 4-pt). Also note there is a huge positive swing for Red on White’s 55 or 65 next turn after Red’s 3/off/, 2/off.
If White does not hit the exposed checker after 3/off, 2/off then Red becomes a huge favourite. If she does hit, she will probably have a strong but takeable redouble to four next turn.
It is hard to calculate this over the board but those two extra checkers off plus the swings on White’s big numbers next turn should lead you to the right answer which is 3/off, 2/off. The safe play is an error but not a blunder. 5/off is a triple blunder.