From Episode 10 of the Death Note (DN) anime series, “Doubt” “Utagau”, in English Dubbed.
L, in a bid to profile Light’s behavior, challenges him to a game of tennis, with both having previously been tennis champions (L being one in Britain), only to quit. During the game, they question in their thoughts regarding whether if Kira is Light and if L is really L. L determines that if Light attempts wins the match (typical of a sore loser, which L suspects Kira is), then he must be Kira; simultaneously if he purposely loses the match (to not create suspicion) he could be Kira also. Light determines that if he wins the match then L would assume that Light is Kira, so he aims to lose the match to not create suspicion. At the same time, they think that in order to get confirmation that their identities are true, they’ll “have to go to Task Force headquarters”. As the whole school watches the match, an opportunity is found, and Light takes it by slamming the tennis ball underneath L’s racket, declaring Light the winner 6 sets to 4.