Arenas was drafted by the
San Francisco 49ers in the 8th round of the
1951 NFL draft. He played seven seasons in San Francisco from 1951 to 1957. On December 16, 1951 he knocked the
Detroit Lions out of the NFL division championship with 51-yard punt return. He led the NFL with 814 kick and punt return yards in 1951, and also led the NFL in yards per touch in both 1951 (13.1 yards per touch) and 1955 (11.1 yards per touch). After the game, 49ers coach
Frank Albert said of Arenas, "He's the greatest clutch artist I've ever seen. He was the difference between the two clubs today." A newspaper columnist in 1957 described Arenas' value to the 49ers:"Arenas is a valuable man on a pro football team, specifically the 49er team. He is more than a thoroughly dependable player. He is an inspirational holler-guy who can lift flagging spirits; who refuses to be whipped even if the score is top-heavy in the other side's favor. Team devotees feel a sense of complete confidence watching a well kicked ball sail in the direction of Arenas, playing safety. Joe hardly ever bobbles one. On those rare occasions when the spinning ball briefly twists out of his waiting arms, he is on the pellet with the speed of a mongoose." Arenas was "a popular and capable performer" in his seven years with the 49ers. Arenas announced his retirement from football in September 1958, saying he was quitting to devote full-time to his job as a salesman and public relations man for the coffee company, Schilling & Co. After he announced his retirement, the
Oakland Tribune called him "a scrappy little back" who "made up with hustle what he lacked in ability" and became "the most popular player on the 49ers." In seven years in the NFL, Arenas accumulated 987 rushing yards, 675 passing yards, 774 punt return yards, 3,798 kick return yards, 17 touchdowns, six interceptions. His 4,572 career kick and punt return yards was the best in
NFL history at the time of his retirement;
Al Carmichael broke his record in 1958. After retiring from the 49ers, he covered the team for the
San Francisco Call-Bulletin during the 1958 season. In December 1958 Arenas wrote that he had been banned from the 49ers' bench and dressing room for things he had written in his newspaper column. According to Arenas, team owner Vic Morabito claimed that his former teammates "had not appreciated my comments about their playing." In an interview in 1990, Arenas said of his time with the 49ers, "It was something I will always cherish. It was the highlight of my life." ==Later years==