Wiktionary
a. (context simile colloquial English) crazy, demented.
Wikipedia
Boxing hares in slow motion – YouTube
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To be as "mad as a March hare" is an English idiomatic phrase derived from the observed antics, said to occur (some say incorrectly) only in the March breeding season of the European hare, Lepus europaeus. The phrase is an allusion that can be used to refer to any other animal or human who behaves in the excitable and unpredictable manner of a "March hare".
Usage examples of "mad as a march hare".
He was obviously as mad as a March hare but somewhere in that confused mind of his Jake suspected there was a sane reason why he had shot Big Oysters Pok.
She was clearly healthier, physically, but as he quickly discovered, she still was mad as a March hare, still precipitately violent, still very dangerous.
When you added in the fact that the young man in question remained just as mad as a March hare, you could understand why the governor only wanted it to go away, and as soon as possible.
But never fear-he's mad as a March hare, but if anyone can get the job done, he can.