As a general rule, baserunners are able to slide into first base. Most baseball leagues do not have a rule against sliding into first base, but the majority of players frown upon sliding into first base because it is slower than running through the base.

Is it against the rules to slide into first base?

Sliding to 1st Base

Yes, sliding is allowed on first base, but it is not recommended since a batter-runner can overrun the base which is faster. When sliding to first base, the runner is allowed to leave the running lane within a reasonable distance for the purpose of getting on base.

Can you slide feet first in baseball?

Players generally slide feet-first but sometimes also use a head-first technique. Strictly speaking, going headfirst into a base constitutes more of a dive than a slide, but the term "slide" is still commonly used.