The most common and most likely answer to this crossword clue is the 8 letter word EARTHING
I've seen this crossword clue in The Daily Telegraph
E
A
R
T
H
I
N
G
Buddy explains!
The straight part
We know that "running to ground" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case running to ground = earthing.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 EARTHING mean?
EARTHING verb- To connect electrically to the earth.
- To bury.
- To burrow.
- The act or process of placing (something) in the earth; planting; burying
- (holism) The process of connecting with the earth's energy, usually through bodily contact (e.g. walking barefoot), supposed to achieve health and vitality.