The purpose of this paper is to discuss a procedure to assess individual performance in team sports in contexts of preassessment and formative assessment. An authentic assessment procedure based on the observation of players’ actions during matches yielded two performance indices: the efficiency index and the volume of play. A general nomogram is suggested for use with various team sports in order to produce a single performance score combining both indices. Content validity, concurrent validity (.74), and ecological validity are discussed. The interobserver reliability (>.90) of the data and the stability of performance (.88) are also examined. Some conditions are discussed for integrating the assessment procedure to the teaching-learning process with an active participation of the students in the collection and interpretation of the data. The proposed procedure is strictly game oriented and yields information reflecting both motor and tactical skills.