The most common and most likely answer to this crossword clue is the 6 letter word HOWZAT
H
O
W
Z
A
T
Buddy explains!
The straight part
We know that "Umpire responds to this" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case umpire responds to this = howzat.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 HOWZAT mean?
HOWZAT interjection- The cry used by members of the fielding team to make an appeal to the umpire.