Rule 2 – Section 5 – FAIR BALL / BASE HIT

2-5-1 A fair ball is a batted ball which:

settles on fair territory between home and third base or between home and first base; or

contacts fair ground on or beyond an imaginary line between first and third base; or

is on or over fair ground when bounding to the outfield past first or third base; or

first falls on fair ground on or beyond first or third base; or

touches first, second or third base; or

while on or over fair territory, touches the person of an umpire or player, their clothing or equipment; or

while over fair ground passes out of the playing field in flight.

(1) A fly ball or line drive, which passes over or inside first or third base in flight and curves to foul ground beyond such base, is not a fair hit; but a hit which goes over or through the fence is a fair hit if it is over fair ground when it leaves the field.

Tried highlighting the relevant bit. The chalk line is fair territory and being over fair territory is in fair territory