Sportsmanlike describes behaviour in a game that is fair, honest and decent — you follow the rules even when nobody would catch you, you do not cheat to win, and when you lose you shake hands instead of sulking or blaming someone. The -like ending means 'in the way a good sportsman would behave'. In real use you meet the negative far more often than the positive: unsportsmanlike conduct is an actual penalty in American football, basketball and other sports, and people say 'that was unsportsmanlike' quite naturally. Saying 'that was sportsmanlike' sounds a bit stiff and old-fashioned, a bit like a coach in an old film. The word also carries an old-fashioned assumption inside it, because sportsman meant a man; sportsmanlike is still used about women, and nobody blinks, but that is a leftover the language has not tidied up.