Learn the lob in tennis: defensive to gain time and offensive with topspin, with milestones, common mistakes, safety notes and FAQ.
The lob is a high ball you play over the net player into the back court. It has two faces: defensive, when you are under pressure and need time to recover; offensive, when you surprise the opponent with topspin and force them back.
The honest answer to "when is the lob the right choice?": when the opponent is at the net and you cannot place the passing shot cleanly between them and the line. The lob is then the safe way out, as long as it lands deep enough – and it must not be too short or it becomes a gift for the overhead. Mind the rule: a ball touching a line counts as in [3], so you may go right up to the baseline.
A note on context: there are few direct studies on the lob in tennis. A biomechanical study with six top players, which also recorded a forehand topspin lob, found that topspin comes from a vertical racket face at contact and a more upward racket path [1]. An older study on passing shots (including lobs) found that the player's body gives cues before the shot that reveal where it goes – and that advanced players read them better than recreational players [2]. The research on the tennis lob offers no more than that; everything else below is practical standard.
How long does it take? You learn the defensive lob in one or two sessions. Hitting the topspin lob reliably under pressure takes weeks to months (practical experience, not a study).
The lob pays off when the opponent is at the net or moving in. If you are under pressure (late to the ball, from defence), it mainly serves to gain time – then choose a high, deep ball (defensive lob). If you have time and space, you can play it flatter and faster with topspin (attacking lob).
Milestone: In 8 of 10 situations you consciously choose between passing shot and lob.
Do not give away the lob. Prepare as for a normal groundstroke. Cues in the player's body reveal the direction, especially on forehand strokes [2]. That is a good reason to keep the preparation for passing shot and lob the same. (Inference from the study, not a measurement.)
Milestone: A partner cannot tell lob from passing shot before contact in 5 of 10 cases.
On the defensive lob you open the racket face slightly and swing from low to high; the legs help. On the topspin lob you swing steeply from low to high with a more vertical racket face: the biomechanical study names exactly that as the mechanism for more topspin [1]. Trunk rotation, upper-arm and hand movement contribute to racket speed [1].
Milestone: You get 6 of 10 lobs over your net player's raised racket without the ball falling short.
The target is a ball that goes over the opponent and lands in the back third of the court. A ball touching the line counts as in [3]. Too short is worse than too long, as long as "too long" does not go beyond the baseline.
Milestone: 6 of 10 lobs land in the last 2 m in front of the baseline.
After the lob you go into the ready position. If the opponent plays an overhead, you expect a hard ball; be ready. The LTA names as a teaching point: return to the ready position after every shot [4].
Milestone: After 8 of 10 lobs you are back in the ready position before the opponent hits.
Practise the lob as a reaction to an advancing opponent: your partner runs to the net after the ball bounces, you lob over him. That trains timing: only when the opponent moves do you decide. Whoever lobs too early gives it away; whoever lobs too late gets smashed. Count how many of 10 lobs get over the advancing player and add one each week.
A high ball over the net player into the back court. It can gain time defensively or surprise offensively with topspin.
When the opponent is at the net or moving in and you cannot place the passing shot safely.
With a steep upward racket path and a more vertical racket face at contact [1].
Yes. Under the ITF rules a ball that touches a line counts as touching the court bounded by that line [3].
Return of Serve in Tennis: How to Get the Serve Back Safely