HekiTen10 will show you how to make running look natural.
If you feel like your character's running looks unnatural, HekiTen10's tip might help you figure out what's wrong. Complete with a handy in-engine example, the artist's advice is to make the foot trajectory shaped like a bike saddle:
Our feet don't just slide along the ground, they go up at the end of the motion, and if you follow this rule, your animations will definitely look more realistic.
This is a universal tip: Chalermphol Wattanawongtrakool, senior animator at Sony Pictures Imageworks, has the same approach. You can also see what to do with the arms from this little tutorial.
Chalermphol Wattanawongtrakool
See how HekiTen10 uses their own advice in their works on X/Twitter: