Clue: Mo Farah hasn't primarily lost races like these (4-9)
Answer: HALF-MARATHONS
Explanation: Definition: races like these
An anagram (?'lost' doing double duty, or 'races' likewise – but 'like these' might just about be adequate as the definition – especially if the definition is regarded as extended) of 'Mo Farah hasn't L', where the L is 'primarily **L**ost'.