Football is evolving constantly.
Fullbacks have almost disappeared from football.
Teams are spreading out their offenses, and the fullback position is being ditched. The 21 personnel (two running backs, one tight end, two wide receivers) was the standard for decades.
The 11 personnel (one RB, one TE, three WR’s) and the 12 personnel (one RB, two TE’s, two WR’s) popularized in the past few years.
The 11 personnel is the spread standard. Generally, teams often line up their tight end next to a tackle, or split him out wide.
The 12 personnel, which was epitomized by New England Patriots TE’s Rob Gronkowski and Aaron Hernandez when Hernandez wasn’t locked up.
The 12 personnel can be lethal. Tight ends create mismatches, and if two pass-catching tight ends are on the field at the same time, the offense will wreak havoc.
Both personnel groupings enable offenses to have immense flexibility and firepower.