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 wordplay.
'stalwart' becomes 'brick' (I've seen this in other clues).
'over' says to put letters next to each other.
'club' becomes 'bat' (I've seen this before).
'made by' is the link.
(Other definitions for brickbat that I've seen before include "Highly critical remark", "Hostile criticism - missile", "Missile, criticism", "Criticism", "Blunt criticism", "An uncomplimentary remark, or kind of missile", "Building block used as missile", "Critical remark", "(Critic's) weapon" and "Piece of blunt criticism".)