This quick hitter, from former Miami (Ohio) coach Charlies Coles, goes well within a flex offense but it can be run no matter type of offense you employ. A fine play from a great coach. RIP Coach Coles.
O1 dribbles to either side (in our diagram, he goes right). O1 then passes to O4 who has cut from low block to elbow / top area.
As in a normal flex offense, on the pass to O4, O2 makes a flex cut to the opposite low block.
With this play, however, instead of O1 screening down for O5, O5 comes up and sets a backscreen for O1.
O4 throws the lob pass to the point guard, O1.
If the lob is not available, simply get into your main offense. If you do run the flex, O5 can then downscreen for O1 and you are right into your flex set.