Bruce Kluckhohn-USA TODAY Sports
Despite all the talk about the money in NFL free agency—who is worth this, who is worth that—performance is still the thing that actually matters. So, when it comes to free agents, the vast majority of football analysis comes down to one question: Do we believe this player can play?Outside observers understandably believed that Janoris Jenkins could not play. Jenkins has always been a ballhawk and a scouting favorite, but he had played a supporting role in many opposing touchdowns in his time with the St. Louis Rams. Per Football Outsiders Almanac 2016, Jenkins finished the past two seasons 51st (out of 75 qualified cornerbacks) and 66th (out of 77) in success rate—that's the statistical output of a journeyman corner, not a star. So when the New York Giants handed him $28.8 million in guaranteed money on a five-year, $52 theoretical million contract this offseason, it seemed foolish.But freed from Jeff Fisher and Gregg Williams' hooligan brigade with the Rams, Jenkins has been much more disciplined as a Giant. He was even asked to shadow Dez Bryant in Week 1 against the Dallas Cowboys; Bryant finished with one catch for eight yards on five targets.And through four weeks, Jenkins ranks first in Football Outsiders' success rate. He has allowed just 2.6 yards per pass. The sample size is small (18 targets) and influenced by New York's other cornerbacks fighting through injury, of course, but this is still a much better player than we ever saw start for the Rams.No. 1 receivers have a -9.8 percent DVOA against the Giants; No. 2 receivers have a 40.5 percent DVOA. In other words, opposing offenses are about ten percent worse than average when throwing at Jenkins, and about 40 percent better when not. That about sums up the difference between Jenkins and Trevin Wade, who was roundly exploited by the Vikings on Monday night.It was asking a lot for the Giants' spending spree to turn their defense into a lockdown unit overnight. There were too many holes on the 2015 team to patch over in one offseason. Overall, the Giants pass defense is still messy, not only because the rest of the secondary has been hurt but also because of long-ignored deficiencies at linebacker and safety.But if Jenkins can keep playing like this, the Giants will have filled one of the most important holes any team has.