Accept first person being upset before start of big contest (7)
I believe the answer is:
embrace
'accept' is the definition.
(I know that embrace is a more specific form of accept)
'first person being upset before start of big contest' is the wordplay.
'first person' becomes 'me' (first-person pronoun).
'being upset' shows that the letters should be reversed in order.
'before' means one lot of letters go next to another.
'start of' says to take the initial letters.
'contest' becomes 'race' (race is a kind of contest).
The first letter of 'big' is 'b'.
'me' reversed gives 'em'.
'em'+'b'+'race'='EMBRACE'
(Other definitions for embrace that I've seen before include "Hold closely, include" , "Take in arms" , "bear-hug?" , "Hold tightly in the arms" , "Include (in one's arms)" .)