Warning! Tiger possibly bitten half the street! (6)
I believe the answer is:
caveat
'warning' is the definition.
(caveat is a kind of warning)
'tiger possibly bitten half the street' is the wordplay.
'tiger possibly' becomes 'cat' (tiger is a kind of cat).
'bitten' is an insertion indicator (some letters bite into others).
'half' indicates taking half.
'the street' becomes 'avenue' (avenue is a kind of street).
'avenue' with half the letters taken is 'ave'.
'cat' going around 'ave' is 'CAVEAT'.
(Other definitions for caveat that I've seen before include "'Caution, warning (6)'" , "Vacate (anag) - warning" , "A caution, proviso" , "Cautionary warning" , "Reservation" .)