American players — see them briefly in undergarments? (7)

'american players' is the definition.
(American football players)

'them briefly in undergarments?' is the wordplay.
'them briefly' becomes 'em' (abbreviation; 'briefly' suggests a short form).
'in' indicates putting letters inside.
'undergarments?' becomes 'linen' (undergarments might be made from linen).
'em' put into 'linen' is 'LINEMEN'.

'see' is the link.