Predator managed to gatecrash a joint from the basement? (7)
I believe the answer is:
piranha
'predator' is the definition.
'managed to gatecrash a joint from the basement?' is the wordplay.
'managed' becomes 'ran' (I've seen this before).
'to gatecrash' indicates putting letters inside.
'joint' becomes 'hip' (hip is a kind of joint**).
'from the basement?' says the letters should be written in reverse (in a down clue, letters go up).
'a'+'hip'='ahip'
'ahip' back-to-front is 'piha'.
'ran' placed within 'piha' is 'PIRANHA'.
(Other definitions for piranha that I've seen before include "Efficient flesh remover" , "Small carnivorous freshwater fish" , "Voracious river fish" , "Voracious tropical fish" , "Small voracious carnivorous fish" .)