Great question, Pete. It doesn't happen often.
Josh Gordon produced immediately for Cleveland in 2012, starting 13 games (and playing in all 16) to catch 50 passes for 800+ yards and five scores.
Prior to Gordon, though, you have to go all the way back to Rob Moore (1990, Jets WR) and Bobby Humphrey (1989, Broncos RB) to find real production as a rookie.
My theory as to why is both the late start these players compared to their rookie counterparts selected 2.5 months earlier and the fact that these players aren’t often young and immature, as their eligibility for the supplemental draft implies.
@Rob Rang can you remember a time where a player was selected in the supplemental draft and went on to make a big impact as a rookie?
Beal joins a Giants secondary that could use help on the perimeter, as well as one suddenly facing the possibility of losing standout Janoris Jenkins, given his recent off-field issues.
While lacking ideal straight-line speed to remain at cornerback, Alexander is a quality player, showing instincts, agility and physicality as a hitter. At minimum he should help Washington’s special teams, and given the club’s struggles with open field tackling in the back end in recent years, Alexander could get an opportunity to help quickly, perhaps back at safety where he played early on with the Hokies.