The most common and most likely answer to this crossword clue is the 12 letter word PERSPIRATION
I've seen this crossword clue in The Daily Telegraph
P
E
R
S
P
I
R
A
T
I
O
N
Buddy explains!
The straight part
We know that "Exercise and sport in air, running around causing this" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case exercise and sport in air, running around causing this = perspiration.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 PERSPIRATION mean?
PERSPIRATION noun- The action or process of perspiring.
- (by extension) Hard work.
- A saline fluid secreted by the sweat glands; sweat.