Disrupt Spell

You attempt to interrupt a creature in the process of casting a spell. The creature makes a Constitution saving throw. On a failed save, the spell dissipates with no effect but the creature can use its reaction to cast a cantrip or another spell with the same casting time as the original spell. This new spell must be cast at a spell level equal to or less than half the original spell slot. If the original spell was cast with a spell slot, the slot isn't expended.

The GM may determine that a monster's attacks are spell-like attacks and can thus be counterspelled (and affected by other abilities that trigger off of spell attacks). If you counterspell a monster's use of multi-attack with these spell-like attacks, it loses all attacks but can use its reaction to make a single spell-like attack.