The East Kingdom’s handbook of youth combat rules is clear and succinct, but it relies on marshals picking up a bunch of additional context during their training.
By contrast, the YC Marshal’s Handbook from Æthelmearc is quite a bit longer, and includes valuable guidelines for youth training, combat techniques, and tournament structures.
Much of that additional material is relevant to youth combat marshals from any kingdom.
My thanks to Mistress Arianna of Wynthrope for her work in assembling this resource.