Bank hosts a track-and-field event (5)
I believe the answer is:
relay
'track-and-field event' is the definition.
(relay race is a track-and-field event)
'bank hosts a' is the wordplay.
'bank' becomes 'rely' (to bank on is to rely on).
'hosts' indicates putting letters inside (inserted letters are welcomed or hosted).
'rely' placed around 'a' is 'RELAY'.
(Other definitions for relay that I've seen before include "Receive and pass on - race" , "Team of workers" , "Broadcast" , "article in bank" , "Hand, pass on" .)