4. OG Justin Pugh
One of the first moves made by former general manager Dave Gettleman was to let both Justin Pugh and Weston Richburg walk in free agency in order to free up cap space to sign Nate Solder, completely destroying the Giants' offensive line at the time.
Left tackle was certainly a need for the Giants, but to completely tear down the rest of the offensive line to sign an aging veteran is a hilariously bad idea. Imagine how much better the Giants could have been if they had opted to sign a lower-cost tackle and retain these two.
While Richburg would only remain in the NFL for two more years before retiring in 2019 due to injuries, Pugh has remained one of the more solid offensive guards in the league over the last five seasons for the Arizona Cardinals.
Pugh has hinted at potentially reuniting with the Giants down the road, however, he never should have left in the first place. Having a consistent guard like Pugh on a rebuilding Giants team would have gone a long way in the development of Daniel Jones and Saquon Barkley.