Knights aren't gladiators. Full armor is effective in the context of a larger fight.
Individually, a knight on foot isn't catching anyone and can probably be poked until exhausted with any stick longer than whatever weapon he's carrying.
Mounted, someone in the ground has little to no chance at all if the horse is capable of moving. On clear ground, the horse is the weapon.
From the wiki page on Agincourt:
"Recent heavy rain made the battle field very muddy, proving very tiring to walk through in full plate armour. The French monk of St. Denis describes the French troops as "marching through the middle of the mud where they sank up to their knees. So they were already overcome with fatigue even before they advanced against the enemy". The deep, soft mud particularly favoured the English force because, once knocked to the ground, the heavily armoured French knights had a hard time getting back up to fight in the mêlée. Barker states that some knights, encumbered by their armour, actually drowned in their helmets.["
Individually, a knight on foot isn't catching anyone and can probably be poked until exhausted with any stick longer than whatever weapon he's carrying.
Mounted, someone in the ground has little to no chance at all if the horse is capable of moving. On clear ground, the horse is the weapon.
From the wiki page on Agincourt:
"Recent heavy rain made the battle field very muddy, proving very tiring to walk through in full plate armour. The French monk of St. Denis describes the French troops as "marching through the middle of the mud where they sank up to their knees. So they were already overcome with fatigue even before they advanced against the enemy". The deep, soft mud particularly favoured the English force because, once knocked to the ground, the heavily armoured French knights had a hard time getting back up to fight in the mêlée. Barker states that some knights, encumbered by their armour, actually drowned in their helmets.["