Throughout his nearly two decades coaching the New England Patriots, Bill Belichick has used a number of odd team building strategies. For example, Belichick used to have the team practice during spring camp without numbers to try to force them to know each other on a personal level (this tactic was eventually banned by the NFL).
This year was no exception, as Belichick handed out non-traditional jersey numbers to all of his rookie players. Running back Sony Michel had 51, quarterback Danny Etling had 58, receiver Braxton Berrios had 55, and cornerback Keion Crossen had 59, among others. All of these numbers are illegal for each player to wear in a game due to the NFL rules that mark certain numbers for certain positions (for example, quarterbacks can only wear 1-19).
Now obviously, due to NFL rules, all of the rookies will receive traditional jersey numbers, likely by the beginning of training camp in July. However, this is an interesting practice by Belichick. It forces these rookies to put aside their pride and vanity and focus on football. Instead of coming into the locker room and spending time on their number and their clothes and other accessories, they are handed obtuse numbers and told that those other things are all privileges, not rights. It also helps band the rookies together. The rule was applied to all rookies, regardless of draft position. Everyone from their first overall selection Isaiah Wynn down to their last signed undrafted free agent was included, which shows the players that none of them are guaranteed anything. They are in it together and need to prove themselves regardless of their past pedigree.
This is certainly an antiquated coaching style, but it is just one of the many little things that have made the Patriots the most successful franchise of the past 18 seasons.