Field athlete with marathon sweater (4,6)
I believe the answer is:
long jumper
'field athlete' is the definition.
'long jumper' can be an answer for 'athlete' (I've seen this before). I am not sure about the 'field' bit.
'with marathon sweater' is the wordplay.
'with' means one lot of letters go next to another.
'marathon' becomes 'long' (marathon can mean long or lengthy).
'sweater' becomes 'jumper' (I've seen this before).
'long' put next to 'jumper' is 'LONG JUMPER'.
Can you help me to learn more?
(Other definitions for long jumper that I've seen before include "garment that comes down over the thighs?" , "Athlete" , "one that can touch his knees?" , "what covers his or her thighs?" .)