The most common and most likely answer to this crossword clue is the 3 plus 4 plus 3 plus 4 letter word RUN LIKE THE WIND
I've seen this crossword clue in The Times
R
U
N
L
I
K
E
T
H
E
W
I
N
D
Buddy explains!
The straight part
We know that "to go in haste" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case to go in haste = run like the wind.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.