Critical remark made by stalwart over club (8)
I believe the answer is:
Here is my best explanation:
'critical remark' is the definition.
(I've seen this before)
'stalwart over club' is the subsidiary indication.
'stalwart' becomes 'brick' (I've seen this in other clues).
'over' means one lot of letters go next to another.
'club' becomes 'bat' (bat is a kind of club).
'made by' is the link.
(Other definitions for brickbat that I've seen before include "Missile, criticism", "Critical remark", "An uncomplimentary remark, or kind of missile", "Building block used as missile", "Hostile criticism - missile", "Highly critical remark", "Blunt criticism", "(Critic's) weapon" and "Piece of blunt criticism".)