I meant to mention as this sub-thread developed that "your horizon should never be level for action and people"
These are not landscapes that you are shooting here. So slavish devotion to levelling is most likely counter-productive and reduces the impact of motion and action in your photos. Whereas *introduction of tilt* is probably something you want to do in many many situations. Look around at highly expert photographers and you will see introduction of tilt, whether the subject is motor-sports, modelling, portraiture, wedding, various sports (in the right situation) and more. The reason tilt is done is it makes the resulting photos better. Tilt does't have to be done on every photo everywhere, but good use of it enhances your output. Once you start doing it you will soon realize you are faced with deciding how much tilt to introduce and which of two directions, so you have to experiment and see what works. And of course you can introduce or moderate tilt in post to taste.