Hi Paul. Cryptic definition. "Legal highs" usually refers to drugs but a trampoline also "pushes" (another drug reference) one up into the air for a "high" which is also legal.
Ah! I went to sleep thinking about AB's clue and came up with it being something on the lines of pushing the Laws (legal) of gravity up in the opposite direction to the Law itself physically in a legal way,
Ab, I liked the misdirection of the drug references. To tell you the truth I never got Iit on first read but with physics and lateral thinking it was a clear winner in my book.