Antonio Brown's return (and subsequent departure), an expert Jon Gruden impersonator and Darren Waller's emergence highlighted the third Hard Knocks episode covering the 2019 Oakland Raiders' training camp.

Brown has been suffering from frostbitten feet while battling the NFL to use an old helmet no longer allowed. As a result, his time at training camp has been limited.

However, the wideout made his return to Napa, California, in this episode, and he even gave former AFC North rival (and current teammate) Vontaze Burfict a hug upon his return.

Burfict played for the Cincinnati Bengals before heading west, and he notoriously leveled Brown with an illegal helmet-to-helmet hit in the 2015 playoffs.

Maurice Moton of Bleacher Report noted the exchange:

However, the helmet issue came to the forefront as Brown no-showed a camp session in the midst of trying to find league-approved headwear.

General manager Mike Mayock's "all-in or all-out" press conference preceded the show's ending, which featured Brown catching one-handed passes:

Elsewhere, comedian and impersonator Frank Caliendo brought his patented impersonation of head coach Jon Gruden to camp and performed in front of the team (warning: video contains profanity):

"Jon Gruden. University of Dayton. I do this s--t for free!" Caliendo said when asked to give his name, school and signing bonus in the fashion of a typical rookie.

Hard Knocks' most profound moment featured potential breakout tight end Darren Waller, who used drugs heavily, bounced back and is in line to be the team's starter come Week 1.

Levi Damien of Silver & Black Pride captured the most jaw-dropping quote:

The Baltimore Ravens picked him in the sixth round of the 2015 NFL draft out of Georgia Tech. He was suspended for violating the NFL's substance-abuse policy twice: once for four games in 2016 and the second time for a full season in 2017.

The 26-year-old landed on the Ravens' practice squad before the Raiders picked him up in November 2018. In limited action, Waller caught six passes for 75 yards.

MJ Acosta of NFL Network gave Waller strong praise for his honesty:

Other fans noted how many compliments teammates and coaches provided about Waller during the episode, leading to a belief that his fantasy football stock will be on the rise:

Warren Sharp of Sharp Football Analysis provided more schematic insights:

Waller is currently listed first on the team's depth chart at tight end.

The episode also featured the Raiders' 33-26 win against the Arizona Cardinals during Week 2 of the preseason. They led 26-0 in the second quarter before the Cardinals closed the gap late.

The penultimate Hard Knocks episode will air Tuesday at 10 p.m. ET on HBO.