Yes, STOPPING is a Scrabble word!

Letter values in Scrabble US: S 1, T 1, O 1, P 3, P 3, I 1, N 1, G 2.

Is it a valid word?

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

fastener consisting of a narrow strip of welded metal used to join steel members
the kind of playing that involves pressing the fingers on the strings of a stringed instrument to control the pitch

come to a halt, stop moving
put an end to a state or an activity
stop from happening or developing
interrupt a trip
cause to stop
prevent completion
hold back, as of a danger or an enemy; check the expansion or influence of
seize on its way
have an end, in a temporal, spatial, or quantitative sense; either spatial or metaphorical
render unsuitable for passage
stop and wait, as if awaiting further instructions or developments

Also: give up, lay off, stop over, break off, turn back, hold back, block off, block up, hold on.