The most common and most likely answer to this crossword clue is the 8 letter word DEPUTISE
I've seen this crossword clue in The Sunday Telegraph
D
E
P
U
T
I
S
E
More clues leading to the result DEPUTISE
- Provide cover for places around India swamped by river
- Take over resolution of dispute with ease at first
- Substitute for topsy-turvy exercise in river
- Some in the audience sit up, edgily backing substitute
- Stand in place on island in river
- Stand in river maintaining exercise, upright
- Stand in river going over back exercise
- Substitute ill-suited to holding record
- Stand in place one’s found in river
- … substitute messes it up, edgy about defending
Buddy explains!

The straight part
We know that "substitute" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case substitute = deputise.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 DEPUTISE mean?
DEPUTISE verb- To make (someone) a deputy; to officially empower.
- To make or name as a substitute.
- To act as a deputy.