Spear and Shield Fighting Techniques?

Sep 2017
United States
Hey all, I was wondering where to start looking for spear and shield fighting techniques, as I do a full-contact recreational game and I'm looking to transition to spear and shield.

I fight in a late Roman unit, so we use clipii shields and carry spatha-type swords. We've also been drilling in formation with the spear; as a unit, with spears extended in rows, we're usually able to wipe the enemy off the field in a flat area just by charging together. When we hit the enemy with our spears and shields, we can switch to the spatha for closer contact.

However, terrain and player availability means we aren't always able to fight in formation. Normally I'd just drop the spear and go with the spatha, but I know countless armies throughout history utilized spear and shield, not least of which being the vaunted Greek Hoplites.

Any sources or historical fighting techniques I could emulate to begin taking on this style?