I didn't realize that Croom went down, just saw that half way through the race there was only one red rider on the track - and that doesn't work well in a Madison.
The rider who is not in the race (i.e. after the hand-off) is referred to as on relief until he drops back down into the race.
Basic tenants of Madison: Never go between two riders on the same team - always go above them (so they can hand off). After the hand-off, make sure the track is clear before heading up-track. (it sounds simple in concept, but gets harder with lack of Oxygen when going far above my lactate threshold).