Growing up in Beaumont, Texas, Kelcher was more interested in playing baseball, even though youngsters in Texas who were big typically played football. He was supposed to be eight years old to play peewee league. However, Kelcher was bigger than his peers, and the Little League president next door got him in a year early. He started playing football in junior high school. Entering high school, he was only interested to play baseball, but the coaches placed him into football.
Kelcher was known for his immense size. Standing 6 feet 5 inches (1.96 m), he once said his weight varied between 280 pounds (130 kg) and infinity. He 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. In nine seasons (1975–1983) with the Chargers, Kelcher was selected to three Pro Bowls (1978, 1979 and 1981), twice as a starter. He 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. In the Epic in Miami, the 1981 divisional playoff which became one of the greatest football games ever, the Dolphins were leading 38–31 in the fourth quarter and threatening to score again at the Chargers' 20 when Kelcher stripped the ball from Miami's Andra Franklin and San Diego's Pete Shaw recovered the fumble. The Chargers rallied to force overtime and won 41–38.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 retired in November 1983, but remained on the Chargers reserve list. The Chargers traded him to the San Francisco 49ers in March 1984. Kelcher had wanted to play again, but not with San Diego. The trade reunited him with former Charger teammates Billy Shields, Johnson and Dean. In his final NFL season that year, the 49ers won Super Bowl XIX.
Kelcher was a favorite among Chargers fans, who greeted him at home games with cheers of "Loueeee". Chargers quarterback Dan Fouts called him "the most universally beloved guy on our team." Kelcher was among the first NFL defensive lineman to weigh 300 pounds (140 kg). He was inducted into the San Diego Chargers Hall of Fame (now the Los Angeles Chargers) in 2003, and the Breitbard Hall of Fame in 2006.
↑ 2.02.12.2Graney, Ed (July 17, 2003). "Chargers Hall of Fame finally finds space to fit in Big Louie". The San Diego Union-Tribune: p. C-1. "Kelcher once said his playing weight fluctuated between 280 and infinity, depending on the buffet special being offered."
↑Brown, Brian (March 29, 1984). "Chargers deal Kelcher to 49ers for low picks". The San Diego Union: p. C1. "Kelcher also told Charger linebacker Cliff Thrift, a friend, that he wanted to return to football but did not want to play again for the Chargers."
↑Magee, Jerry (February 26, 2006). "Chargers fans had love affair with 'Loueeee'". The San Diego Union-Tribune: p. C-6. "'Loueeee,' Chargers crowds at Qualcomm Stadium crowds would coo, lovingly. 'Loueeee.'"
↑Magee, Jerry (November 10, 2003). "Seems like old times, circa 1980s". The San Diego Union-Tribune: p. C-6. "Fouts showed up to offer a few words at halftime on the occasion of Kelcher being received into the Chargers Hall of Fame."