My mare has learned a new nasty habit. I've had her almost 3 years and in the last couple of months she's decided that its appropriate to kick at other horses when they are walking by and she is either tied, or on lead. She pulled this stunt last night after I'd stopped lunging in the arena to pick up poop. It was kind of busy in there with a trainer and some people using their horses as lawn chair watching. I'd just picked up her poop and was waiting for the doorway to clear. She was relaxed, head down, chill, with a loose lead. One of the other girls brought her horse in to ride, and walked him past her, he wasn't super close, but my mare, totally relaxed, suddenly springs into action, backs up, squeals and boots him for no apparent reason. She's been in close quarters with this gelding many times, leading past him in the isle, or using the outdoor wash rack together, and never once had a problem. Never laid an ear or mare stare at him. She has threatened at one of the other geldings when he is loping past her in the arena a couple of times, swung her hip at him while I was riding, and obviously got a hard boot and a swat and growl to correct her. 2 weeks ago she was tied in the isle, and decided to back up at her pasturemate who was walking back, but I assumed its because it was her herd mate that she tends to pick on in the pasture. She got corrected and swatted for that too. Lately she has been trying to assert her authority in pasture with the others. she is out with 7 other horses, and is somewhere near the top of the pecking order. Its like she is boss mare in training. When she came to the barn, she was the bottom of the pecking order and got picked on all the time. its like she suddenly has had enough and now chases the others. She has backed up and tried to boot at them when they crowd her at the gate (ok, makes sense, they are in her space and trying to get towards the gate (or her person at the other end of the lead) and she also tries to chase the others away from me. She always gets a hard correction and a swat with the lead, but its clearly not enough. there was no indication that she was a) in a bad mood, b) in heat, c) in pain when she booted this gelding. It just happened out of the blue when she looked completely relaxed. In all instances she does not like horses coming up behind her, and used to get bit on her bum all the time but it seems she got fed up and isn't having it anymore. HOW DO I STOP THIS? I feel like I have corrected her, but not hard enough. obviously I was unconcerned about her kicking and wasn't prepared for it when she did it, but I would like to know that I can get it in her head that this is NOT acceptable. the horse she kicked is worth 10 x more than her and has a career. She's just my pain in the butt that I amuse myself with.