The most common and most likely answer to this crossword clue is the 4 plus 4 letter word TEAM MATE
I've seen this crossword clue in The Times
T
E
A
M
M
A
T
E
Buddy explains!

The straight part
We know that "Fellow back on the field maybe" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fellow back on the field maybe = team mate.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TEAM MATE mean?
TEAM MATE noun- One who is on the same team.