The most common and most likely answer to this crossword clue is the 11 letter word GREENKEEPER
I've seen this crossword clue in The Times
G
R
E
E
N
K
E
E
P
E
R
More clues leading to the result GREENKEEPER
Buddy explains!
The straight part
We know that "Groundsman" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case groundsman = greenkeeper.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 GREENKEEPER mean?
GREENKEEPER noun- An employee responsible for the maintenance of a golf course.