It's the hormones talking. It's the cute version of the teenage hormonal rabbit. You might want to spay / neuter your rabbit before it evolves into the less cute biting / spraying urine / phantom pregnancy rabbit (and the even less cute dying of ovarian cancer rabbit if your rabbit is a girl). If your rabbit is a male and that circling your legs is all he does you can just leave it - just be careful when you and other people walk, as those rabbits can be silly and get themselves stepped on running around our legs without looking were they are going...