Chap twice given a forage crop (7)
I believe the answer is:
alfalfa
'forage crop' is the definition.
(I've seen this in another clue)
'chap twice given a' is the wordplay.
'chap' becomes 'alf' (short for Alfred).
'twice' indicates the doubling of some letters.
'given' means one lot of letters go next to another.
'alf' duplicated is 'alfalf'.
'alfalf'+'a'='ALFALFA'
(Other definitions for alfalfa that I've seen before include "food plant" , "Lucerne, a fodder plant" , "cattle feed" , "odder plant" , "A forage plant" .)