が速い

is fast

→ が
phrase Common #5,031
is fast Follows the thing or action whose speed is being described; が marks it as the subject.
JA: この電車は走るのが速い。
EN: This train is fast.

テンポが速い

It’s fast-paced.

— セッション (2014)

このあたりは流れが速い。

The current is swift around here.

再生が速い

The playback is fast.

— Demon Slayer -Kimetsu no Yaiba- The Movie: Mugen Train (2020)

この川は流れが速い。

This river has a fast current.

彼は、足し算が速い。

He is quick at addition.

男性は計算が速いと言う。

They say that men are quick at math.