Yes, PIT is a Scrabble word!

Letter values in Scrabble US: P 3, I 1, T 1.

Is it a valid word?

PIT is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a sizeable hole (usually in the ground)
a concavity in a surface (especially an anatomical depression)
the hard inner (usually woody) layer of the pericarp of some fruits (as peaches or plums or cherries or olives) that contains the seed
(Christianity) the abode of Satan and the forces of evil; where sinners suffer eternal punishment
an enclosure in which animals are made to fight
(commodity exchange) the part of the floor of a commodity exchange where trading in a particular commodity is carried on
(auto racing) an area at the side of a racetrack where the race cars are serviced and refueled
a trap in the form of a concealed hole
a surface excavation for extracting stone or slate
lowered area in front of a stage where an orchestra accompanies the performers
a workplace consisting of a coal mine plus all the buildings and equipment connected with it

Also: infernal region, nether region, stone pit, orchestra pit, play off.