Tennis FAQ

Picking the right stroke matters because each one is read against its own sequence. Forehands, backhands and returns follow a groundstroke pattern: ready position, unit turn, load, racquet drop, forward swing, contact out in front, follow-through and recovery. The serve has its own pattern built around the toss, the trophy-position load, the racquet drop behind your back and full extension at contact. The volley is read as a short punch with a small turn and no big backswing.

The choice also decides which checks are allowed to apply. A groundstroke check such as a weak unit turn is never applied to a serve, and a volley is not marked down for a short follow-through, because a volley is meant to be short.

Overheads and smashes are not a separate tennis option in Motion Lab, so there is no dedicated read for them yet.

A serve travels up rather than across, so a frame sized tightly to your body cuts off the top of the toss and the contact point, which is exactly where the serve is judged. Guided recording keeps the serve in landscape and asks for extra space above your head: step back until your full overhead reach fits. A portrait clip is still analyzed, with a gentle note suggesting landscape. A clip whose rotation is wrong, so that you appear on your side, is different: Motion Lab says the video looks sideways and does not score it, so rotate it and try again.

1. Place the phone side-on or behind you in landscape, far enough back that your feet and the top of your reach both fit.
2. Hold it steady on a tripod, a bag or the fence — not in a hand that follows the ball up.
3. Finish any ball bounces, then hold your stance still for a second before the toss.
4. Keep the whole motion in view: stance, toss, trophy position, racquet drop, contact and the landing.

If the terms are new, see trophy position and racquet drop.

Side-on is the clearest view of your unit turn and where contact happens relative to your body. Behind works too, as long as the full stroke and the contact stay visible. Whichever you choose, use the same spot when you retest.

Groundstrokes move you sideways, so frame wider than feels necessary. A clip that crops you as you run to the ball loses the ready position and the recovery, and the tennis read scores both. Keep filming for a beat after contact: a clip that ends right at the hit cannot be read at all, and Motion Lab asks you to re-film it; one that ends just after contact leaves your recovery and next-ready position unscored.

Use a fixed camera rather than zoomed-in footage that follows you around the court, and 60 frames per second if your phone offers it.

The tennis card in Motion Lab lists shoulder turn, racket-path arc, contact-point timing, follow-through and pelvis movement proxy. All of them are estimates from one camera. The racquet's path is mostly projected from your hitting arm; the head is only traced where it shows up clearly in the frames. Contact timing comes from when your hand reaches peak speed, not from seeing the ball meet the strings.

The issues it can raise include early or late contact, an incomplete unit turn, a follow-through that brakes too soon, and a downward path through contact on a groundstroke.

Tennis points do not stop at the hit, so when the clip is long enough the read also looks at the movement around it: whether you started from an athletic ready position, your spacing to the ball, how you recovered, and whether you got back toward a ready spot for the next shot.

What it does not claim: measured racket face, ball spin and precise contact point. The per-sport breakdown is on how video analysis works.

What it can speak to is the direction of your swing through contact. A downward path on a groundstroke is flagged because it tends to produce unwanted slice or balls into the net, and the coaching points you toward a racquet drop and a low-to-high swing.

The racquet trace shown on your clip is an estimate. It follows the racquet head where the head was picked out in the frames; where it never was, it follows your hand or is labeled as projected out along your forearm. The card says which. Treat it as a direction, not a number.

Spin rate and ball speed need a dedicated sensor or radar. For the ideas behind them, see topspin and racquet face angle at contact.

One difference is worth knowing. The racquet path is estimated from a single hitting arm, so on a two-hander, where both arms drive the racquet, treat that path as a rougher guide than the body reads.

Film side-on, which shows the unit turn and the contact point best, and stand far enough back that both arms, the racquet and your feet stay visible through the whole swing. On a two-hander the second arm is part of the stroke, so do not let it slip out of the frame.

The terms are explained under one-handed backhand and two-handed backhand.

Volley: you can film closer than for a groundstroke, because volleys are compact, but keep the racquet, your hands and the contact point in view. Checks that assume a full swing, such as a long follow-through, are switched off for volleys, and drills built around a bigger turn are not suggested for them.

Return: the return is mostly reaction — the split step, the first move and a compact preparation. Frame it wide from behind the baseline so both directions stay in shot. Late preparation and late contact are among the checks that apply, alongside the groundstroke checks; serve-only checks never do.

A tennis ball is small and fast, and fast contact blurs at 30 frames per second. Nothing in the analysis depends on finding it: contact timing is estimated from your movement, and there is no ball-speed, spin or landing read from video.

What matters more is you — your whole body and the racquet in frame from the ready position to the recovery. If you have to choose between showing the bounce and showing your feet, show your feet: without them, balance and leg-drive reads are limited.

Filming a feed or a rally is fine. Other players in the shot can pull tracking onto the wrong person, so see who else can be in frame.