It could be because he or she is territorial ie guarding their space from you. Neutering (male) or spaying (female) may help (and is better for them in other ways too). Make sure they have plenty of space to run and jump and that they have places to hide and plenty to do (cardboard boxes make good toys and loo rolls with hay inside). Best of luck. If your rabbit is really shy of being handled you could start by stroking him or her gently with a paint brush and as time goes on and they react less then you can stroke them.