VPT237 High Volley
This drill can handle a large group, a variety of levels and it's a great cardio drill. Players start in one line near the singles sideline and the baseline. The first player runs to the cone and splits then shuffles to the next cone and then hits a closing high volley from the pro's toss. That player then moves around the extra cones and goes back in line.  The next player starts when the first player starts to shuffle.  So the drill moves pretty fast.  For variety you can incorporate different physical activities between the cones on the side for example, a ladder station.  You can also use a variety of tosses moving the player up, back or over.  For safety make sure the players hit the volley down the line.  You can also adjust the space between the cones based on the number of players in the drill.