When an ally that is within 5 ft. of you is attacked by an enemy that you can see, you can use your Reaction to perform the Willow's Ward combat manoeuvre;

• You defend your ally from the attack, using your own body to shield them from this and any subsequent attacks made against them during this turn while redirecting them towards yourself instead. The attack(s) then continue as normal, with you taking damage if the enemies Attack Roll is higher than your own Armour Class (AC), rather than your allies.
• This can be done at any time that an enemy is attacking your ally, but before your ally has taken the damage.