boost their morale

去年のCLの覇者、バルセロナをチェルシーが準決勝で破りました。The Daily Yomiuri(04/26/2012)の24面SOCCER欄から英語表現を拾います。

10-man Chelsea stuns Barca to make CL final

Ramires ran onto a long through ball from Frank Lampard to send an impressive lob over Victor Valdes to calm Chelsea’s nerves and boost the visitors morale as they headed back into the dressing room.
“With 2-0 at halftime we would have believed we could get it but this 2-1 was a little bit psychologically bad for us,” said Guardiora, whose team also lost Gerard Pique in the first half to a concussion. “The penalty we didn’t score and they got stronger.”
Barcelona’s inability to convert its possession advantage into goals was symbolized by Messi’s rare miss from the spot in the 49th, as the Argentina winger has now been held scoreless in seven meetings against Chelsea. Barcelona hasn't been able to beat Chelsea in the last seven meetings,　either.]

boost their moraleで「彼らの士気を高める」という意味(ジーニアス英和辞典、第4版)です。boostと聞くとクルマなどのエンジンの馬力を上げることを思いだしますが、「人の心のエンジン」の馬力upにも使えるということがわかりました。加えて、morale boosterで「士気を高めるもの[事]」(同辞典、第4版)というフレーズも辞書に載っていました。ジョン・テリー選手の退場で浮足立っていたチェルシーにとってラミレス選手のゴールはまさにbest morale boosterだったのでしょう。(EnDough)