A dictionary defines the phrase as "Fig. to put forward arguments against or objections to a proposition-which one may actually agree with-purely to test the validity of the proposition." source.It's the inherent job of the head coach to play devil's advocate with their team's success.
Lotief said, "As a coach you always see the flaws that you need to work on,".
"There's no flaw in the way they compete. I'm just talking about skills-wise. We just have to continue to develop. We're not where we need to be."
Do you think "throw a wet blanket over their team's success" would also work in this context, considering that the coach was trying not to let the success went to the players' heads and keep their feet on the ground?