If the NFL lockout leads to games being canceled, it could be an opportunity for the new United Football League to make a splash. The UFL hasn't tried to position itself as a competitor to the NFL in its first two seasons, but an extended lockout might prompt it to re-think that strategy. Could the UFL sign a college star like Cam Newton and change the pro football landscape? Probably not, but it's not an outlandish possibility considering that some legends did start their career in the so-called "other" league.

No. 5 Joe DiMaggio, PCL

The Pacific Coast League was never considered a major league, but it came pretty close. Before the Dodgers and Giants moved to California in 1958, there were no MLB teams west of St. Louis. This allowed the PCL to feed off local talent and grow into near-major status. Thanks to a recommendation from his older brother, DiMaggio joined the San Francisco Seals as a teenager. During his second season, he hit safely in 61 consecutive games, a PCL record and a sign of great things to come. The following year, he almost ended his career by tearing a ligament while exiting a bus. A Yankees scout believed that DiMaggio could recover from the injury, so he bought Joltin’ Joe’s rights for $25,000. As part of the deal, DiMaggio stayed in San Francisco for the 1935 season. He made the most of it by winning the Most Valuable Player Award and bringing home a PCL title for the Seals. The PCL continued to attract attention even after losing stars like DiMaggion and Ted Williams to the majors. In 1952, it gained “open” status, which meant MLB teams would have a tougher time poaching its talent. This was done in hopes of becoming a third major league. But it faced a swift decline because of MLB's expansion into the West as well as the spread of televised games.

No. 4 Herschel Walker, USFL

After winning the Heisman Trophy as a junior, Walker wanted to go pro. At the time, neither the NFL nor the USFL allowed underclassmen, but USFL owners looked the other way as Walker signed with the New Jersey Generals. He chose New Jersey in hopes that the proximity to New York would generate commercial opportunities. But he only got one ad spot, a joint promotion for McDonald’s and Adidas. He won two rushing titles in three USFL seasons. He drew attention to the fledgling league but many accuse him of causing its demise. Initially, USFL teams planned to stay under a low salary cap and grow slowly. But after Walker's signing, teams grossly exceeded their budgets to sign a number of stars, including Reggie White and Steve Young. Despite the publicity, teams racked up enormous debt, eventually forcing the league to fold. Walker joined the Cowboys and made the Pro Bowl in 1987 and 1988. Despite his contribution in Big D, Walker is now more famous for being traded to the Minnesota Vikings for five players and six draft picks. The deal helped the Cowboys climb to the top of the NFL while Walker disappointed in Minnesota, never rushing for 1,000 yards in a season.

No. 3 Joe Namath, AFL

Namath was drafted by both the St. Louis Cardinals of the NFL and the New York Jets of the AFL. As you know, he decided to sign with the Jets, due in large part to the record-setting $427,000 offered by then-Jets owner Sonny Werblin. Werblin defended the enormous contract (a precursor to the absurd deals inked by today’s rookies) by saying that Namath could be more than a great football player; he could be a star. Namath immediately paid dividends as the 1965 AFL rookie of the year. Of course, his most memorable contribution came in Super Bowl III when he led the Jets over the NFL’s Colts, validating the start-up league after his famous guarantee. His effect on AFL-NFL relations extended beyond that game. Before his decision to join the Jets, the NFL had largely ignored the AFL. After his signing, the bidding wars between the leagues escalated, and teams began to consider signability when deciding on their draft picks.

No. 2 Julius Erving, ABA

Despite his transcendent play, Erving was considered by some as being responsible for the demise of the ABA. While under contract with the Virginia Squires, Erving also signed a contract with the Atlanta Hawks, even though the Milwaukee Bucks owned his NBA rights. Chaos ensued, but Erving ended up staying in the ABA with Virginia. After a few years, the Squires were forced to sell Erving to the New York Nets, and he led them to two ABA titles. In 1976, the NBA and NBA merged. Many claimed that Erving was a main reason for the merger, saying that the NBA wanted to Erving and that the only way to get him was to take the whole ABA. Originally, the Nets intended to keep rolling in the NBA with Erving, but the cost of the fees to join the NBA forced them to sell him to the Philadelphia 76ers. Erving helped them reach the NBA finals four times but won just once.

No. 1 Wayne Gretzky, WHA

At the time, the NHL required players to be at least 20, so a 17-year-old Gretzky began his pro hockey career in 1978 with the Indianapolis Racers after signing a $1.75 million contract. He netted his first goal in the fifth game of his career and his second goal came just four seconds later. But he played just eight games with the Racers, who had to sell The Great One to Edmonton due to financial problems. On his 18th birthday, he signed a 10-year contract, the longest in hockey history up to that point, with the Oilers. He was named the rookie of the year after leading the Oilers to the best record in the WHA. Edmonton lost in the WHA finals to the Winnipeg Jets in 1979, the league's final season. The Oilers were among four WHA teams absorbed into the NHL, but some critics questioned whether Gretzky would succeed in the established league. He immediately proved them wrong by winning the Hart Trophy as league MVP in his first season. Gretzky then re-wrote the NHL record book while helping the Oilers win four Stanley Cups in five seasons before the controversial trade to Los Angeles.