I think that "bashing a jagged hole" refers to the man's body bashing a hole in the hedge when he falls into it.
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Kapahi GPY,you mean the hedge is like a spear which digs into his body?"spearing himself on it" refers to the hedge piercing his body (I suppose it has sharp branches), while "bashing a jagged hole", as far as I can tell, refers to the damage his body does to the hedge, not the other way around. It would be quite odd to say that a hedge "bashed a jagged hole"