Strange ruling on cleave

[Psyduck]

In a recent campaign I was in, I had a character that had cleave. I used an attack that dropped an opponent to -1 hp, and my DM ruled that I could cleave because my opponent fell. I brought up a good question afterward.

Does cleave allow an attack after anything that'll "drop" an opponent say, a trip attack or knockdown?

 

[Jeremy]

As clarified by the Sage, no. Trip, Improved Trip, Knockdown, and the like do not meet the requirements for a Cleave attack. This is one case in which the descriptive text is meant to be evocative in a literary sense and is not to be interpreted literally. If you reduce a creature to -1 hp or less and they drop you get a cleave.

 

[Dr. Zoom]

I would only allow you to cleave when you drop your target below 0 hp. Tripping would not allow a cleave, and the S&F errata clarifies that successful knowdowns do not allow for a cleave, either.