Kelcher was known for his immense size: he stood 6'5", weighed 285 pounds, wore size 17EEE shoes, and had a size 16.5 ring finger. He was drafted in the 2nd round in 1975 and was named to the NFL All-Rookie team. Kelcher was selected to the Pro Bowl in 1978, 1979 and 1981; was named All-AFC in 1977, 1978 and 1980; and 1st-team All-Pro in 1978 and 2nd-team All-Pro in 1977, 1980 and 1981. In 1977, his teammates voted him the team's Most Valuable Player.
Kelcher was sidelined in 1979 for all but three minutes after a knee operation. He returned in 1980, teaming with fellow 1975 Chargers' draftees Fred Dean and Gary "Big Hands" Johnson as the Chargers led the NFL in sacks (60). Johnson and Dean were named 1st-team All-Pro, with Kelcher being named 2nd-team All-Pro. The trio, along with Leroy Jones formed a defensive frontline that was locally nicknamed the Bruise Brothers. In the 1980 AFC Championship Game against the Oakland Raiders, Kelcher has 20 tackles, 10 solo and 10 assisted, and also one sack.Don "Air" Coryell's Chargers teams of that era are mostly remembered for its high-scoring, pass-oriented offense. The Chargers won the AFC West from 1979–1981 and made the playoffs in 1982.
Kelcher finished his career in the 1984 season as a member of the Super BowlXIX champion San Francisco 49ers, reuniting him with former Charger teammates Johnson and Dean.
^"No. 16: Chargers' best draft class". ESPN.com. March 28, 2009. Retrieved May 27, 2011. The 2001 class was good, but the 1975 class ranks the best. San Diego had four of the first 33 picks in the draft, and the Chargers selected three defensive linemen that would form the nucleus of "The Bruise Brothers" and once formed three-fourths of the AFC Pro Bowl defensive line.(subscription required)
^Smith, Rick (1981). 1981 San Diego Chargers Facts Book. San Diego Chargers. p. 45.