The most common and most likely answer to this crossword clue is the 4 letter word TILL
I've seen this crossword clue in The Guardian
T
I
L
L
Buddy explains!

The straight part
We know that "work in field" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case work in field = till.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 TILL mean?
TILL preposition- Until; to, up to; as late as (a given time).
- To, up to (physically).
- To make it possible that.
- Until, until the time that.
- A cash register.
- A removable box within a cash register containing the money.
- The contents of a cash register, for example at the beginning or end of the day or of a cashier's shift.
- A tray or drawer in a chest.
- To develop so as to improve or prepare for usage; to cultivate (said of knowledge, virtue, mind etc.).
- To work or cultivate or plough (soil); to prepare for growing vegetation and crops.
- To cultivate soil.
- To prepare; to get.
- Glacial drift consisting of a mixture of clay, sand, pebbles and boulders
- Manure or other material used to fertilize land
- A vetch; a tare.