A singles or doubles team that wins all four Grand Slam titles in the same year is said to achieve the Calendar Year Grand Slam.

It is so difficult due to the varying courts that are had to play on as well as the level of competition at each event.

Only 6 singles players have won the Grand Slam. 7 doubles teams have won.

To pitch the perfect game, the pitcher does not allow any hits, walks, or hit batsmen. In short, "27 up, 27 down".

It is so difficult because the pitcher has to not only avoid throwing down the middle, but also avoid walking anyone.

There have 17 perfect games by modern definition. That's 1 approximately every 8 years or about 1 every 11,000 games. No pitcher has thrown more than one.

Shooting a 13-under 59 is one of golf's most exclusive clubs.

Only 4 men have shot a 59 in US PGA Tour history (3 if you don't count Mickelson's unofficial event). Annika Sorenstam shot one on LPGA tour in 2001.

The Triple Crown consists of three races for three-year-old thoroughbred horses and that achievement has been rare in recent years.

It is so difficult due to that horses have to be 3 years old (officially all racing horses have their birthday on January 1st of the year), the short time span in between races (14 days off vs. the typical 30-60 days off), and the differences in track length.

There have only been 11 triple crown winners. None since 1978. However, Big Brown may have the best chance in a long time this coming Saturday.

The perfect NCAA Basketball season has a team winning all their regular season games as well as the NCAA tournament.

Even if a team makes it through the regular season unscathed, the NCAA tournament is full of upsets which have to be negotiated.

Only 7 NCAA basketball champions have have ended with perfect records. The last one was by the '76 Indiana Hoosiers coached by Bob Knight.

The Modern Grand Slam in golf is achieved by winning all four of golf's Major championships in the same calendar year. When the The Masters was founded, it started the "Modern Grand Slam". This is different from the PGA Grand Slam of Golf which refers to a tournament of all the winners of the four major championships.

It is so difficult due to the varying styles of courses and the level of competition at each one.

No golfer has ever acheived a modern Grand Slam. Tiger Woods has been the closest by winning all 4 consecutively, but over two calendar years. Bobby Jones won what would have been the "traditional Grand Slam" by winning all four major golf events of 1930.

To qualify, a team must finish the regular season and the post season without a loss.

It is so difficult due to the parity in the NFL combined with the durability required.

Only the '72 Dolphins have ever achieved this feat. Though the 2007 Patriots went longer undefeated, at 18-0, they were handed their first loss in the Superbowl preventing them from completing this feat.