Double Trouble originally was a ball machine drill suggested in TennisPro Magazine by Inaki Balzola, PTR's International Director. It's a great doubles drill for large groups. Players should be able to rally.
One player is at ad side baseline; coach is at same baseline on deuce side. All other players are at the net post. Coach feeds first ball to first player waiting at net post. This player volleys the ball back toward the coach. Coach feeds second ball cross court; same player must run and volley toward player waiting at baseline.
Player at baseline lobs this volley over net player. Net player runs down the lob, returns it with a lob of their own, goes to end of player line. Note baseline player does not have to play this ball. Coach then stars the process all over again with next player waiting in line.
Continue for a set time or until X amount of lobs have been hit by either player; then rotate a different player into the baseline position.
Eliminate first fed volley; volleying player only gets one ball fed before baseline player returns it with a lob.