take a dent

昨日の取り組みで、綱取りの大関鶴竜は隠岐の海に押し出されてしまいました。

Sumo: Kakuryu falls to 1st defeat, Hakuho, Haruma heating up

OSAKA (Kyodo) -- Ozeki Kakuryu's yokozuna bid took a dent on Tuesday as he was handed a first defeat at the hands of rank-and-filer Okinoumi on the third day of the Spring Grand Sumo Tournament.

Yokozuna Hakuho, meanwhile, feted his 29th birthday in style with a demolition of youngster Endo, winning convincingly on the day that also marked the third anniversary of the 2011 Great East Japan Earthquake.

http://mainichi.jp/english/english/newsselect/news/20140311p2g00m0sp063000c.html

take a dentはそのままだと「くぼみが付く、へこみができる」ですが、相撲の文脈ですので、「（痛い）初黒星を喫す」あたりでしょうか。（UG）