尻部 meaning in English

croup

If your elbows and upper arms are not connected to your torso , the rein contact will enter your body at the shoulder level , which allows the horse to use the leverage of your torso against you , e . g . by rooting against the bit and pushing his croup up , which renders your seat and rein aids completely ineffective
如果骑手肘部和上臂不能和踝联系，那么缰联系只能到你的肩膀，这样马就会利用你的踝的杠杆左右来对抗，马匹对抗衔铁，抬高尻部，从而导致你的骑坐和缰扶助完全失去效果。