If Liverpool really wants to the title race, then on nights like that Benitez is going to have to be more adventurous with his substitutions.
If you want to win, you have to bring on strikers, in place of midfielders, or defenders. It is no value simply replacing a striker for a striker, a winger for a winger, or a midfielder for a midfielder. Bringing forward players off as Benitez did is a holding pattern tactic.
Ironically, bringing on another striker for a defender is a good move, because although it creates risk at the back, thats exactly when you are more likely to score, on the counter, after Westham have gone forward.
With the defensive way Liverpool played, Westham were never going to have a crack, and Benitez did nothing to offer them encouragement. Babel and Ngog were fine to come on, but Rierra and Keane should not have been taken off. Sacrifice at the back, more than likely you will still hold out to a Westham team intent on a draw, but you increase the chances of scoring.
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