Squad leaves at start of Macbeth (4)
I believe the answer is:
team
'squad' is the definition.
(I know that squad can be written as team)
'leaves at start of macbeth' is the wordplay.
'leaves' becomes 'tea' (as in tea leaves).
'at start of' says to take the initial letters.
The first letter of 'macbeth' is 'm'.
'tea'+'m'='TEAM'
(Other definitions for team that I've seen before include "Cooperating group" , "Competitive side" , "Group or squad" , "Two or more working together" , "(Sports) side" .)