If you can read portugese:
.:: CENIPA ::. In short: rapid vertical takeoff to avoid persons, causing loss of control.
This however doesn't really add up with the video footage, I can't see anybody on the ground in the video prior to the crash. At ~ 1:20, the low RPM is already going off briefly, that should have been already a warning that power is at the margin. To me, the whole thing looks more like the guy got irritated by hitting the ground hard and then overpitched instinctively.
Just my 2 cents anyway.