A racket having a handle, a frame attached to the handle, and strings with two perpendicular strings stretched in the frame, running back and forth in the frame. The system also includes: for each string, a piezoelectric sheath coating said string along most of its length, said sheath being divided along its length into at least three piezoelectric areas capable of each generating an independent voltage according to mechanical stress exerted on the strings; and an electronic circuit connected to the piezoelectric areas of the strings to identify a portion of the strings submitted to the highest mechanical stress according to the voltages generated by the piezoelectric areas of the strings.