It's not knowing what you can run as quick hitters but selecting virtually any quick hit option, set play, or inbounds play, and diagramming one, two or three cuts on into the flex's 2-3 formation. That's the beauty of the flex, passing game, shuffle or box type offense. Essentially any symmetrical offense can be entered after any set play or inbounds simply by moving one or two key players. Many teams play box out of bounds. I like the cross because it allows screening in multiple directions and two directional cutting.
Many teams run a box and use a screen the screener principle to get a player open.
In the cross, imagine your 3 man taking the ball out of bounds at mid sideline right. Put your 5 man in the middle of the cross near the elbow slightly extended. PG guard starts low block, 2G starts out top in a line with 5 and PG, and your 4 man begins on the weak side block. When any defender tries to help the PG pops out high, or the 5 man can step to the ball. If 5 is pressure, we back pick 5 with the 4 man.