Arriving at an acceptable definition for "aggressive" may be the most difficult and contentious aspect of this article.
For our purposes, an aggressive player is one who is willing to put pressure on an opponent on every shot. Although the placement and speed of the shot play a part, more central to the idea of applying pressure is an ability to hurry the opponent. Typically, an opponent is hurried because an aggressive player takes the ball early or comes to net.
"Aggressive" is not a synonym for "effective," as many of the most effective players, such as Rafael Nadal and Novak Djokovic, exercise patience and use selective aggression to finish off points. Patience typically is not a virtue of the most aggressive players.
Furthermore, an aggressive player is not necessarily a hard-hitter, and a hard-hitter is not necessarily an aggressive player. John McEnroe, one of the most aggressive players in tennis history, was by no means a big hitter.
Prime examples from the past of what we consider aggressive players are Boris Becker, McEnroe, Pete Sampras, and, if you go way back, Jack Kramer.
Only one American made our top-10 list, although Mardy Fish and John Isner might rank 11th and 12th.
The debate about Robin Soderling is not whether he is aggressive enough to deserve a spot on the list, but whether he is on the tour at all.
He has not played a match in more than a year, first because of a wrist injury, then because of mononucleosis. He said late last year in an ESPN.com interview, that he might return in 2013, but has not done so yet. It seems, at age 28, his career may be over.
If he were on tour, he would rank among the top four or five most aggressive players, because he goes for broke on nearly every shot. He overpowered Roger Federer at the French Open in 2010.
With Soderling now unranked because of inactivity, we leave him on the fringe at No. 10.
Though considered an all-court player who can survive long baseline rallies, Roger Federer is willing to take balls early and come to net.
He is an excellent volleyer, and can serve and volley on occasion. He also has an ability to play balls on the rise to force opponents into hurried responses.
Federer is the most aggressive of the four elite players on the ATP Tour. Rafael Nadal, Novak Djokovic and Andy Murray rely more on their baseline consistency and their shot-making off their groundstrokes.
However, Federer often is content to remain the baseline and win long rallies, which is why he is only ninth on the list.
Milos Raonic poses a problem when assembling this list.
He may have the biggest serve in the game, often resulting in a weak return that enables him to step into the court and smash a quick winner. That's the epitome of aggressiveness.
However, Raonic does not routinely follow his serve to net, and he is sometimes content to rally from the baseline during his opponent's service games.
In some matches he comes to net often. In others, he seldom approaches.
Measuring his aggressiveness becomes difficult, but the power and effectiveness of his serve are enough to land him at No. 8.
Feliciano Lopez is a bit of an enigma because he has the two key components of a classic aggressive style—a big, effective serve and a good net game—but does not always employ them.
He often takes a defensive position from behind the baseline, and uses a slice backhand, looking very little like an attacking player.
He is very capable of employing a serve-and-volley game, however, and can attack the net effectively during rallies as well. Some (including myself) feel he should rely on that style more.
As a Spaniard who grew up on red clay, committing to an attacking game may be difficult.
Fernando Verdasco is on the list because he seems to go for a winner on nearly every shot.
Seldom is he just keeping the ball in play. Instead he tries to hit the line and end the point, no matter what his position on the court may be.
Although Verdasco is a baseliner, his points usually don't last long. When he is hitting his shots, he's difficult to beat. It makes him a streaky player, and he can take himself out of matches when his shots start going awry.
Jo-Wilfried Tsonga is fun to watch because he is willing to try so many types of shots at virtually any point of a match.
Part of his arsenal is a serve-and-volley game that he will use on occasion. He is not afraid to attack the net and use his varied volleying skills to apply pressure and keep an opponent off balance.
Rafael Nadal once said it was difficult to play Tsonga because an opponent can't get a rhythm against him. That hints at Tsonga's aggressive style, which eschews patience for a willingness to attempt attacking shots from a variety of angles, often at unexpected times.
Like many such aggressive players, especially ones as athletic as Tsonga, opponents are almost defenseless when he gets on a roll.
Nicolay Davydenko is aggressive in a very different way from the classic serve-and-volleyers such as Boris Becker and Pete Sampras.
Davydenko is more like John McEnroe and Andre Agassi in that his aggressiveness comes from his ability to hurry his opponent.
Davydenko is not a great volleyer and his serve is not outstanding. He lives on the baseline for the most part.
However, he does not plant himself yards behind the baseline and wail away from near the back fence. Instead, he stands near the baseline, sometimes inside it, taking the ball early, allowing him to create splendid angles while rushing his opponent.
Opponents are on the defensive on each shot.
Now ranked No. 41, Davydenko, at age 31, is not the factor he was in 2006, when he rose to No. 3.
Michael Llodra is one of the few remaining serve-and-volley practitioners on the tour, and he's probably the best player still using that approach. That alone ensures him a place high on this list.
The volley is the ultimate symbol of aggressive play, and Llodra may be the best volleyer in men's tennis today. His left-handed serve and deft play at the net are reminders of some of the great aggressive players of the past.
His style makes him an outstanding doubles player, and he has won three Grand Slam doubles titles.
Though he has slipped significantly in the rankings, James Blake remains dangerous because of his style.
"Bold" is the best way to describe Blake's approach. He never tries a safe shot, always opting for a high-degree-of-difficulty shot that may end the point. Blake's opponent is always under pressure, partly because he knows Blake will attempt something unthinkable by most foes.
Blake has a big serve, which keeps opponents off balance, and his shots are never defensive. Every one is designed to end the point. He often adds some pizzazz to his play, making his shots appear even more aggressive.
His style is one reason his ranking has fluctuated so much.
Tomas Berdych goes for a winner on virtually every shot. Never does he take a defensive approach.
He takes balls early, hits them with tremendous pace and frequently comes to net to try to finish points early.
Points are short in matches involving Berdych. Either he hits a winner, or he makes an error. Opponents often are irrelevant to the outcome. If Berdych is making a lot of his shots, many of which are low-percentage attempts, he will win. If he is committing errors, he will lose.
Opponents typically just wait him out. The top players often have the wherewithal to survive his onslaughts.