The most common and most likely answer to this crossword clue is the 7 letter word BEANBAG
I've seen this crossword clue in The Guardian
B
E
A
N
B
A
G
More clues leading to the result BEANBAG
- Habitually complain about second-class seat
- Maybe runner has to reserve soft seat
- Runner perhaps needing to reserve somewhere to sit
- Headcase split support for student?
- Bishop began to perambulate about area round seat
- Cushion blow at first — each dreadful bang …
- Furniture made by headcase!
- 9 land on head
- Comic character with gossip overturned cushion
- To put on head, secure large cushion
Buddy explains!

The straight part
We know that "seat" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case seat = beanbag.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 BEANBAG mean?
BEANBAG noun- A piece of soft furniture consisting of a leather or vinyl covering stuffed with dry beans or other similar pellets.
- A small cloth bag filled with dry beans, used as a toy or for exercising the hands.
- A type of juggling ball usually made from leather or cloth stuffed with dry beans.
- (usually in the plural) A testicle.
- An idiot.