The 65th Indianapolis 500 on May 24, 1981, is one of the most debated finishes in race history. The Rookie Orientation Program was introduced that year and the race was permanently moved from Memorial Day to Sunday, which made that year's date the earliest the race had ever been run.

The rainy month cut short or eliminated several practice days and extended pole qualifying over three days. It was also a month of calamity. Rick Mears suffered extensive burns from a pit fire on Lap 58 when fuel spilled out of the hose, drenching Mears, his mechanics and the engine, which caused it to burst into flames. Danny Ongais' fiery crash on Lap 63 in the Turn 3 wall left him unconscious and with compound fractures to both legs that kept him from competing for the rest of the season and left him with a permanent limp.

But that May was good to Bobby Unser. The Penske driver's speeds continually topped the charts, he grabbed the pole and led the most laps. His pit crew won the Miller Pit Stop Contest. Unser was the race winner — until he wasn't — and then was again.

On Lap 146, a deflating tire caused Tony Bettenhausen to touch wheels with Gordon Smiley, whose car spun backwards into the wall in Turn Four. Mario Andretti, in a Patrick Racing Wildcat, and second-place Unser pitted. Unser exited first.

As he left the pits, Unser passed anywhere from seven to 14 cars on the apron, eventually blending into the queue at the exit of Turn 2. Andretti followed Unser until he realized the illegality of the move and tucked into line in the short chute. He radioed his crew that Unser had passed under yellow.

No penalty was assessed to either driver, but both moves were caught on film and commented on by the TV announcers (after the fact, since commentary was added later for tape-delayed airing). Despite reports from observers, USAC officials declined to issue penalties. Unser took the checkered flag just 5.3 seconds ahead of Andretti. He was the winner that day.

The next morning he wasn't. After reviewing the tape, officials issued Unser a one-lap penalty for incorrectly exiting the pits. This dropped Unser to second place, making Andretti the winner. It marked the first time a 500 winner had been stripped of victory.

Roger Penske, Unser's team owner, launched a lengthy protest and lawsuit, arguing that the wording of the code Unser violated, the "Blend Line Rule," was vague. (The "Blend Line" was a new rule that supposedly instructed the drivers where to get in line under yellow conditions as they exited the pits, but the wording was so unclear that everyone had a different interpretation.) Unser reasoned that as long as he stayed below the white line, he could pass cars until the Turn Two blend line.

Although some people believe both Unser and Andretti should have been disqualified and the win given to third-place finisher Vern Schuppan, Unser's penalty was rescinded, partly due to ambiguity in the blend rule and partly because officials believed that the call should have been made during the race in order to allow Unser an opportunity to overcome a penalty. As Penske's lawyer put it, the penalty had to fit the crime.

Unser was fined $40,000 for the passing infraction when his win was reinstated on Oct. 9. It was his third career Indy 500 victory — and the last time he raced at Indianapolis. Bitter over the controversy and subsequent loss of commercial endorsements, the 47-year-old, Indy's oldest winning driver, retired from racing at the end of the season, stating in a 1982 interview: "Regardless of the outcome, it's been ruined for me."

According to rumor, Mario kept the winner's ring. He told Motor Trend, "Maybe I didn't deserve to win the race, but neither did he. The rule was clear, and a rule is a rule. Bobby won the race, but he cheated. There's an asterisk next to that one."

Contested 500s — the 1911 race

Contested 500s — the 1963 race

Contested 500s — the 1966 race

Contested 500s — the 2002 race