Fanatical attack around Beachy Head (5)
I believe the answer is:
rabid
'fanatical' is the definition.
(I know that fanatical can be written as rabid)
'attack around beachy head' is the wordplay.
'attack' becomes 'raid' (raid is a kind of attack).
'around' indicates putting letters inside.
'head' indicates taking the first letters.
The first letter of 'beachy' is 'b'.
'raid' placed around 'b' is 'RABID'.
(Other definitions for rabid that I've seen before include "Fanatical, infected" , "Raging (having been bitten by a dog?)" , "Furious like mad dog?" , "extremist" , "Extremely fanatical" .)