Repeated sprint ability (RSA) is the capacity to produce several short sprints with brief recovery and lose as little speed as possible. Matches sometimes demand exactly this in intense passages of play.
RSA depends on both maximal sprint speed and aerobic fitness, which helps recover phosphocreatine between efforts
A typical test is around 6 sprints of 30-40 m with about 20-25 seconds of recovery, scored on best time, mean time and decrement
Training it directly works, but so does improving speed and the aerobic base separately
Long sets of very short-rest sprints are highly fatiguing and belong in limited doses