The most common and most likely answer to this crossword clue is the 4 plus 7 letter word SHIN SPLINTS
S
H
I
N
S
P
L
I
N
T
S
Buddy explains!
The straight part
We know that "lower-leg complaint" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case lower-leg complaint = shin splints.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.