From Wiktionary, the free dictionary
From horse racing, the horses and the jockeys.
runners and riders pl (plural only)
- (humorous, idiomatic) The candidates in a competition or leadership contest.
15 December 2019, Jamie Grierson, Heather Stewart, “Labour leadership contest: who are the runners and riders?”, in The Guardian[1]:Labour leadership contest: who are the runners and riders?
