How do I grapple/throw in Mortal Kombat 1?

Absent user1887158 providing the actual information from the manual, page 10 of the game manual states (emphasis mine):

When in close quarters

Additional moves used in close quarters are the knee, the head blow, and the throw. All three are highly effective, and do not require the full limb extension which is impossible in close quarters. Although these moves are potent, they can only be used when directly adjacent to an opponent.

Basically get in close (using the D-pad), and use the punch button (default C on the original Dreamcast controller) to throw your opponent.

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