Here is a basic bracket to support a 10" deep shelf on a standard 1" pitch pegboard. I'm using 1/4" plywood cut into 10x24" pieces on a tablesaw.

At exactly 10", the wood fits firmly between the outer lip of the bracket and the pegboard. It's stable without the need for additional hardware to attach the shelf to the bracket.

These seem pretty robust, but probably couldn't handle a huge load. Use good judgement.

Designed in Freecad. Source file is included. Feel free to modify.

UPDATE, August 2019: I changed the shape of the pegboard hooks slightly to increase strength.