During free agency and the 2021 NFL draft, the majority of the teams stocked up players in one of the most important positions on the team: the offensive line. The O-line isn't just responsible for protecting the quarterback and keeping them upright, but also for creating gaps for the running backs to exploit. Some teams already had strong offensive lines, while others used free agency and the NFL draft to make theirs better than it was last season.5 Teams with the best offensive linesHere are the teams with the best offensive lines going into the 2021 NFL season:#1- Cleveland BrownsThe Cleveland Browns are at the top of this list simply because they will be bringing back all five offensive linemen from the 2020 season. The Browns have slowly built their O-line over the last few seasons and it paid dividends last season. Jack Conklin, Jedrick Wills, Joel Bitonio, J.C. Tretter and Wyatt Teller have all been exceptional for the Browns. They also drafted James Hudson in this year's draft for added depth at tackle and guard.#Browns offensive line continues to show its dominance https://t.co/3EcDxnmWnK— Dawgs By Nature (@DawgsByNature) May 24, 2021#2 - New England PatriotsIn 2020 the New England Patriots had the best run-blocking O-line in the NFL. The Patriots did lose Joe Thuney to the Kansas City Chiefs, but they also got Trent Brown back. The Patriots also have Michael Onwenu, who had an impressive rookie season in 2020.Patriots OL Mike Onwenu says he doesn't have a preference between guard and tackle. He primarily played right tackle in 2020 after playing guard in college. He projects at left guard in the current offensive line but has worked at both positions.— Doug Kyed (@DougKyed) May 25, 2021#3- Tampa Bay BuccaneersThe reigning Super Bowl champion Tampa Bay Buccaneers have been able to bring back all of their starters, in all positions, for the 2021 season. As for the Buccaneers' offensive line, Tom Brady has become comfortable with Ryan Jensen at center in his first year with the Bucs.Left guard Ali Marpet, left tackle Donovan Smith, right guard Alex Cappa and right tackle Tristan Wirfs formed a dominant O-line that helped the Buccaneers win the Super Bowl last season. "Tom Brady was a complimentary piece here. This run game, this offensive line, this defense was the show."More from the crew on the @Buccaneers Super Bowl win. pic.twitter.com/qX82DuT0Bv— GMFB (@gmfb) February 8, 2021#4- Indianapolis ColtsFor multiple seasons in the past, the weak point for the Indianapolis Colts offense was the O-line. But over the past few years, the Colts have used the NFL draft to build a solid offensive line that they hope will help reignite Carson Wentz's career. The Colts offensive line consists of Pro Bowl center and guard duo, Ryan Kelly and Quinton Nelson, as well as Julien Davenport. #Colts QB Carson Wentz has been sacked 119 times since 2018.Over that same span, Indy’s offensive line only allowed 72. pic.twitter.com/nPiKpm0pzX— Locked On Colts Podcast (@LockedOnColts) May 19, 2021#5 - Kansas City ChiefsThe Kansas City Chiefs' O-line's poor play was one of the reasons why Patrick Mahomes struggled in the Super Bowl. Due to injuries, the Chiefs' offensive line was made up of backups and players that switched positions. This offseason, the Chiefs have completely reconstructed their O-line.The Chiefs brought in Orlando Brown from the Baltimore Ravens and signed free agent Joe Thuney to a five-year deal. The Chiefs also signed Kyle Long, who came out of retirement to play for the Chiefs and also signed former Los Angeles Rams center Austin Blythe.Kansas City Chiefs’ offensive line should be in NFL’s top 10 says national columnist https://t.co/EyiimsDRyj— The Kansas City Star (@KCStar) May 25, 2021