Place one's shirt at risk? (6)
I believe the answer is:
gamble
'risk?' is the definition.
(gamble is a kind of risk)
'place one's shirt' is the wordplay.
I cannot quite see how this works, but
'one's' could be 'am' ('one is' can humorously mean 'I am') and 'am' is found in the answer.
This explanation may well be incorrect...
'at' is the link.
Can you help me to learn more?
(Other definitions for gamble that I've seen before include "Wager; sounds like frolic" , "Take a chance, speculate" , "Take risks" , "Take a risk" , "Bet money" .)