Is Robinson a Saints fan? If so I'd start him. If not him, it's likely to be a debutant which is equally high risk.
I reckon he'd be more likely to do something an inexperienced teenager might do in such a game, such as lunge into a stupid challenge, if he was brought on as a sub trying to make an impression.
Choosing our lineup for the derby will be a massive headache for Will. The timing is far from ideal as so many of our players are still mostly unknown quantities at this level.