2 ways that friction can be used in a structure?

Friction is important for all sports.

Without it it becomes really hard to accelerate

For example a 100m sprinter.

It would be great for him if there wasnt any air resistance (as long as he can breath).

But he needs friction on the floor to push himself forward.

However friction is less useful in hockey, skiing, and almost all types of boarding(Snowboarding, wakeboarding, kneeboarding,