Yeeeeah.... there is a limit to the "do not judge by appearance" shtick. It's just about mass, and a small rabbit has so little mass it's practically not possible for them to do anything against something like a tiger or buffalo. No matter how much the rabbit accelerate to increase the impact, it would destroy the rabbit before it could hurt the bigger animal.
And yes I know it's a cute comic but my brain just won't let it be.
MidaranaKitsune, the thing is... yes, you are right. But you still need to agree that she attacked his chin, and with great accuracy you don't need much mass behind the kick to make opponent drop out. Of course it was only possible when he wasn't ready for this.
MidaranaKitsune did hit the point on the head. Although Judy would have had to have some training for through the academy to handle takedowns of those bigger and stronger than her, the movie usually showed her using her speed and combining it with using her opponent's strength or size against them to gain the upper hand.
Even so, I wouldn't count out Judy. Although I'm surprised though how many Zootopia comics keep showing up. Good stuff though.