I saw this thread a while ago and sort of struggled with it, went looking and could find nothing authoritative, and am reporting back that I’m unsure how to respond. But if forced to choose, I have to say that I don't agreed that this interference.
The commentary in the LL Rules Instruction Manual for Rule 6.05 (which is taken from the full text of the OBR rule) states: “If a bat is thrown into fair territory and interferes with a defensive player attempting to make a play, interference shall be called, whether intentional or not.” But I think that requires the thrown (i.e., moving) bat to interfere with the player. An analogy can be drawn to a concept found elsewhere in Rule 6.05, which is that it is interference if a thrown bat hits a batted ball but not if the batted ball just rolls into the stationary bat. That admittedly does not directly apply, but the underlying logic might.
Compare the original question to this only slightly different situation: If the batter hadn’t carried the bat anywhere, but just dropped it right in front of the plate when taking off for 1B, what if the catcher then stepped and tripped on it when first moving out from behind the plate to go after the ball? I don’t think I’d consider that to be interference.
Extending that reasoning, here, the player tripped over the apparently stationary bat. Absent some indication the batter intentionally positioned the bat to hinder the defense, I’m thinking the correct call is:
“Hey, catcher, does your ankle hurt?”