Adam Monteiro is an offensive lineman who was undrafted out of Boston College in 2019. The 25 year old player is listed on the Commanders website at 6’7” and 320 pounds, and has spent time with three teams over 3 NFL seasons.
The Commanders website lists Monteiro as a tackle, but he seems to have positional flexibility.
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As you can see from the chart above, per PFF, Montiero took snaps at three positions in the 2021 preseason — 32 snaps at right tackle, 29 at right guard, and 5 at left tackle.