Definition of go long:
(v) :
(finance, intransitive) To buy a financial product, such as a share, so as to profit from a rise in its value; compare go short.
(v) :
(sports) To run far from the person throwing a ball in order to receive a long pass; (especially American football, Canadian football) to run down the field away from the quarterback to receive a long or Hail Mary pass.
(v) :
Used other than figuratively or idiomatically: see go, long.