[UNDER-1 5 b.] The hold obtained by a wrestler who gets his arms below those of his opponent.

1

1870.  J. De Mille, The Boys of Grand Pré School, viii. 122. Then Bruce made a plunge forward, and before the other could guard against it, he had caught him around the waist, under his arms.
  Bruce had got the ‘underhold.’

2

1895.  Funk’s Stand. Dict.

3