Roger Federer has 16 Grand Slam (GS) titles, which is the most anyone has won so far. He should be crowned the GOAT.
He has achieved the career slam, something which is missing from the CV of the great Pete Sampras, who has the second largest haul of GS titles, with 14.
But there are two factors which place a question mark over Federer's eligibility to be crowned the GOAT.
The first one is the most discussed one. His adverse head-to-head record against Rafael Nadal.
Nadal, then a mere 17-year-old, beat Federer in Miami at their very first meeting. Federer was then 22 and the World No. 1.
The young Spaniard proved it was no fluke, eventually taking away the great man's crown and beating him in the grand slam finals on three different surfaces. Nadal's head-to-head against Federer is 17-8, with 7-2 being the grand slam subset.
If a man cannot be the best in his era, how can he be the best of all time?
The second factor against his being crowned the GOAT is also often discussed but not nearly quite as often as the first.
It is the contention of many tennis observers that Federer played in a weak era between 2003 and 2007, which allowed him to pile up his huge haul of GS titles. I subscribe to this view.
To prove this hypothesis, I will set out some definitions and assumptions.
Weak era means there was only one great player in his prime playing during those years.
A player is in his prime from the calendar year in which he turns 22 to the calendar year in which he turns 29.
So Federer's prime is from 2003 to 2010, and Nadal's from 2008 to 2015.
The prime years assumption is roughly based on the age-performance of elite tennis players, as per studies done by Schulz and Curnow, as well as by me.
A great player is one who wins at least three GS titles by the end of his career.
The requirement for three titles is a rule of thumb criterion based on what might be called the rule of three.
We have the Latin saying, "omne trium perfectum" i.e., "Everything that comes in threes is perfect." There's also the unforgettable Goldfingerism: "Once is Happenstance. Twice is Coincidence. The third time it's Enemy action."
Even common sense would seem to support the rule of three. A player could win a slam because of a series of favorable factors. It could happen again, but if it did happen a third time we have to acknowledge that the player is really better than the rest of the field.
The field is the players taken as a whole.
Because of the hundreds of players in the field, the quality of the field would change very little over a few years and can be taken to be constant over, say, 10 years.
In other words, an average Top 10 or Top 30 or Top 50 or Top 100 player in 2003 is likely to be equal to the average player in any of those categories today.
So what does a weak era mean?
It means a period of time when there were less than two greats in their prime playing during those years.
As per this definition, 2001-2002 had no greats, as Sampras and Andre Agassi were post-prime and Federer was pre-prime.
The years 2003-2007 were also weak because there was only one great in his prime, Federer, playing during those years. Agassi was post-prime and Nadal was pre-prime.
The years 2008-2011 are strong because of the presence of Nadal and Federer in 2008-2010 and Novak Djokovic from 2009-2011. Djokovic is not counted for 2008, as he was pre-prime, and Federer is not counted for 2011, as he is post-prime.
It may be noted that a great player doesn't have to win his three titles during the years we are attempting to classify. He has to be in his prime during those years, and he has to win three GS titles by the end of his career.
So classification of an era as weak or strong will often be on the basis of hindsight.
A weak era would be characterized by the lack of a rivalry and strong era would be characterized by a rivalry (or trivalry, or an even rivalry among more than three people) i.e. the same set of players would be appearing frequently in grand slam finals.
For instance, earlier it was Federer and Nadal who were frequently in finals. Today it is Nadal and Djokovic.
This is because the two are better than the rest of the field.
Between 2003-2007, there wasn't another player who could consistently defeat the field and reach the finals. In other words there was no other player in his prime who was a great.
The concept of prime is important because before prime, a player is not at full strength, lacks sufficient experience and emotional maturity and his game is still developing. Post-prime, the player is in physical decline. There can be deemed to be strong competition for GS titles when there are at least two greats in their prime.
But there is no doubt that this is one of the strongest eras ever, as evidenced from the same four people being year-end Top 4 since 2008.
At least two of the same four made it to the semifinals in virtually all the grand slams. Not to mention the fact that all the grand slam titles from 2004 (except three) have been shared between Federer, Nadal and Djokovic.
The strength of this era is also evident from the fact that the Top 4 are so far above the field that between them they have about 41,000 points, an aggregate matched by the points of players 5 to 22 or 23.
So while there is no doubt Federer is one of the greatest, we cannot classify him as the greatest based on just his grand slam haul.