It is a bit strange in this sentence. However, it comes from the following phrase:
A bird in the hand is worth two in the bush.
Meaning, having one bird in your hands, presumably to eat, is better than seeing two birds in the bush (which you would have to catch before eating).
So I would interpret your sentence in this way: Being hit in the head in that manner, is worse than being hit (in some other less dangerous way) twice.