Run behind float (4)
I believe the answer is:
raft
'float' is the definition.
(raft is a kind of float)
'run behind' is the wordplay.
'run' becomes 'r' (cricket abbreviation).
'behind' becomes 'aft' ('aft' can be a synonym of 'behind').
'r'+'aft'='RAFT'
(Other definitions for raft that I've seen before include "Simple boat" , "Simple floating structure" , "vessel" , "A whole lot" , "large collection" .)