Begging to take place of boxing instructor initially (9)
I believe the answer is:
suppliant
'begging' is the definition.
(thesaurus)
'take place of boxing instructor initially' is the wordplay.
'take place of' becomes 'supplant' (I've seen this before).
'boxing' means one lot of letters goes inside another ('box' can mean contain, as in to put in a box).
'initially' says to take the initial letters.
The first letter of 'instructor' is 'i'.
'supplant' going around 'i' is 'SUPPLIANT'.
'to' acts as a link.
(Other definitions for suppliant that I've seen before include "One begging" , "One who begs humbly" , "Asking earnestly" , "One making an appeal" , "One praying for a favour" .)