Well, if you managed to detect and track an incoming drone you could ‘jam’ its camera with a high-powered laser - or something that threw up a curtain of flares or burning magnesium, or whatever.
Does that work for a fleet of 10 drones? 100 drones? 1,000 drones?
Not sure why you're being downvoted. Legitimate concern.
A drone swarm dropping hand grenades is like targeted artillery. Experience from WW 1 is that it's straightforward to defend against artillery fire, just retreat into a shelter. A target that's worth five dozen drones with grenades can afford a bunker.
So simple in your scenario... The target just needs to jump in their nearest bunker, better hope they happen to be attacked outside their bunker eh?