Cricketer, one cornered by a reptile, must be agile (9)
I believe the answer is:
acrobatic
'agile' is the definition.
(I've seen this before)
'cricketer one cornered by a reptile' is the wordplay.
'cricketer' becomes 'bat' (I've seen this before).
'one' becomes 'i' (Roman numeral).
'cornered by' means one lot of letters goes inside another (I've seen this in other clues).
'reptile' becomes 'croc' (short for crocodile).
'bat'+'i'='bati'
'a'+'croc'='acroc'
'bati' inserted into 'acroc' is 'ACROBATIC'.
'must be' acts as a link.
(Other definitions for acrobatic that I've seen before include "circus performer?" , "Like a gymnastic entertainer" , "Gymnastically agile" , "Involving physical agility" , "Showing agility" .)