The most common and most likely answer to this crossword clue is the 9 letter word TRACKSUIT
I've seen this crossword clue in The Daily Telegraph
T
R
A
C
K
S
U
I
T
More clues leading to the result TRACKSUIT
- Follow Hearts, maybe training in this?
- In a truck, sit changing gear for practice
- What an athlete may wear in line with action
- Course — leading clubs perhaps put it on for training?
- In practice, one covers one song linked with clubs?
- Sportsperson’s habit to monitor clubs, for example
- What an athlete may wear to follow match
Buddy explains!

The straight part
We know that "In practice, one covers" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case in practice, one covers = tracksuit.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 TRACKSUIT mean?
TRACKSUIT noun- A garment, usually consisting of a top and trousers (commonly known as tracksuit bottoms) worn as an outer layer by participants in sporting events such as athletics. The tracksuit is usually designed to be easily removed or replaced, before or after competing. Tracksuits have also been adopted in some cultures as leisurewear.