The most common and most likely answer to this crossword clue is the 9 letter word CONFORMED
I've seen this crossword clue in The Times
C
O
N
F
O
R
M
E
D
Buddy explains!

The straight part
We know that "toed the line" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case toed the line = conformed.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 CONFORMED mean?
CONFORMED verb- (of persons, often followed by to) To act in accordance with expectations; to behave in the manner of others, especially as a result of social pressure.
- (of things, situations, etc.) To be in accordance with a set of specifications or regulations, or with a policy or guideline.
- To make similar in form or nature; to make suitable for a purpose; to adapt.