Definition of throng in:
(v) :
(transitive, informal) To add something extra free of charge.
(v) :
(transitive, informal) To include in a calculation.
(v) :
(idiomatic) To quit, to fold.
(v) :
Used other than figuratively or idiomatically: see throw, in.
(v) :
(transitive, archaic) To inject, as a fluid.
(n) :
Alternative form of throw-in. [(soccer, rugby, basketball, handball) A set-piece where the ball is thrown back into play]