TUSCALOOSA, Ala. — A simple nod, glance or gesture. This is the reward for learning a complicated 3-4 defense, for upholding a proud tradition, for playing under Alabama Coach Nick Saban for five years.

In teaching moments with younger defenders, Saban turns to Robert Lester, or any other Crimson Tide upperclassman with whom he has won two national championships, for reassurance and confirmation: that Lester had made that mistake, that Saban had been correct in what he said, and that they had been through this before together.

Lester, a fifth-year senior safety, is comforted by a mutual trust — in Saban’s scheme and his own ability. With every player, there were defensive values to be learned. But the fear of displeasing Saban persists, while, as the senior linebacker Nico Johnson said, “We want people to fear our defense.”

This group may be among Saban’s scariest. With seven new defensive starters, replacing six N.F.L. draft picks, the undefeated Crimson Tide have allowed 10 touchdowns in nine games, keeping pace with last season’s unit that led the team to the national championship.