Hello Vincent,
"All of a sudden" might be better at the beginning of the sentence.
"A man who ride" should be e.g. "A man riding a motorcycle".
"Quickly" doesn't quite work; "snatching" implies quickness.
Probably the man would not "run away": he would use the motorbike to escape.
For the last line, it is the thief, not the men in the shop, who is "far away". Thus not "they".
Best wishes,
MrP