Beware being caught by hail (4)
I believe the answer is:
cave
'beware' is the definition.
(old-fashioned term meaning 'look out')
'caught by hail' is the wordplay.
'caught' becomes 'c' (cricket abbreviation).
'by' is a charade indicator (letters next to each other).
'hail' becomes 'ave' (greeting in Latin).
'c'+'ave'='CAVE'
'being' is the link.
(Other definitions for cave that I've seen before include "Hollow - warning" , "Warning - grotto" , "Underground enclosure with surface access" , "hole" , "part of rocky coastline?" .)