In other words, players who come on perform at a higher level than players who come off. If a manager waits for clear signs of fatigue, he might be substituting too late; he might make better decisions by following a set rule such as <58<73<79. During his ill-fated reign at Portsmouth in the 2009/10 season, Avram Grant could have followed that rule in twenty-one games. He chose to do so only four times. On two of those occasions, his team made a dent in their deficit. In the seventeen other games, where he did not follow that rule, the deficit stayed the same or increased fourteen times. If
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