Abstract: Apparatus which indicates various stages of forehand or backhand strokes which are practiced by a tennis player with or without a ball, with or without an opponent and without supervision has a disk-shaped support which is mounted on the innermost part of the handle of a tennis racket, a circumferentially complete rail at the periphery of the support, a carriage which is freely slidable along the rail, and a set of adjustable bells mounted on the support radially inwardly of the rail to be struck by an elastic prong on the carriage in selected angular positions of the carriage, namely, in those positions which designate important parts of the stroke practiced by a tennis player. The carriage can be tied to an elastic band so that the support and its rail normally move relative to the carriage, or the carriage is free to slide along the rail by inertia and/or under the action of gravity.