American went down behind joint (8)
I believe the answer is:
dovetail
'joint' is the definition.
(I've seen this before)
'american went down behind' is the wordplay.
'american went down' becomes 'dove' (US past tense of 'dive').
'behind' becomes 'tail' ('tail' can be a synonym of 'behind').
'dove'+'tail'='DOVETAIL'
(Other definitions for dovetail that I've seen before include "Joint - fit neatly" , "Woodworking joint" , "Interlocking joint" , "Violated (anag) -- mortise joint" , "Type of joint - fit closely together" .)