The most common and most likely answer to this crossword clue is the 5 plus 1 plus 3 plus 2 plus 6 letter word COVER A LOT OF GROUND
I've seen this crossword clue in The Times
C
O
V
E
R
A
L
O
T
O
F
G
R
O
U
N
D
Buddy explains!
The straight part
We know that "to run far" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case to run far = cover a lot of ground.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.