It has been well over two years since former UFC heavyweight champion Cain Velasquez competed in the Octagon. That drought comes to an end Sunday when he squares off against Francis Ngannou in the main event of UFC Fight Night: Phoenix. Ngannou stopped a two-fight losing skid in November and won't have to worry about ring rust, but many of the statistical categories drastically favor Velasquez.

The following is an analysis of the numbers, which could end up being the difference on Sunday.

Striking differential

The average career striking differential for a ranked UFC heavyweight is +0.93. Velasquez is unranked due to inactivity, but in terms of this metric, he is far ahead of the rest of the pack. His career striking differential (significant strikes landed per minute minus significant strikes absorbed per minute) stands at +4.09. To put the number into perspective, his differential is 40 percent higher than the current leader among ranked heavyweights (Alexander Volkov at +2.92).

Ngannou, meanwhile, has the third-worst striking differential among ranked heavyweights at +0.03. Defensively, he allows his opponents to land only 1.94 significant strikes per minute. However, Ngannou lands only 1.97 significant strikes per minute, which is dead last among the top 16 heavyweights. Velasquez's defense is slightly more porous, as he allows his opponents to land 2.29 per minute, but he more than makes up with it in terms of offense. He lands 6.38 per minute, which is more than double the average for ranked heavyweight (2.76) fighters.

If this matchup comes down to who can land the most strikes, Velasquez is in the driver's seat. However, Ngannou has found some success despite not landing with volume. He has averaged only 13.86 landed significant strikes per fight in his seven UFC victories. While often successful despite low volume, Ngannou's style has its drawbacks. He managed to land only 21 significant strikes in a loss to then-champion Stipe Miocic, and in his most recent defeat, he combined with Derrick Lewis to land the second-fewest significant strikes in a three-round fight (31) in UFC history.

If Ngannou can't get on track early, his inability to land consistently will give him major issues. Velasquez has always been an offensive striking dynamo. He should be able to wear down his opponent with volume if he avoids Ngannou's initial offensive output.

Striking position

Francis Ngannou knocked out Alistair Overeem at UFC 218, one of the most vicious finishes in UFC history. Josh Hedges/Zuffa LLC/Getty Images

A key factor behind Velasquez's ability to land with such high volume, while avoiding reprisal from opponents, is his ability to secure and strike from advantageous positions. Most fighters land the largest proportion of their significant strikes at distance, which is defined as standing and not in the clinch. Velasquez, on the other hand, has delivered 38 percent of his significant strikes on the ground and 27 percent in the clinch. Landing such a high number of meaningful strikes on the ground is really what separates him from other heavyweights, since he is able to unleash offense from the top position without suffering damage. During his career, he has landed 283 significant strikes on the ground, while absorbing only nine in this position.

Most of Ngannou's landed significant strikes come at distance (68 percent). He has -- at least statistically -- held his own defensively on the ground. During his UFC career, only 22 percent of the significant strikes he has absorbed have been on the mat.

Velasquez's ability to land strikes on the ground is a vital element of his offense. Ngannou will need to finish the fight early or find a way to avoid the ground striking to defeat the former champion.

Takedowns

Ngannou's career history is somewhat a mixed bag in terms of takedown defense, and he will need to keep things on the feet to be successful here. During his UFC career, he has stopped 70 percent of the takedown attempts against him, which is above average for a ranked heavyweight (62 percent). However, he still has allowed 2.29 takedowns per 15 minutes of fight time. His performance against Miocic is a bit of a microcosm of his takedown track record. Miocic failed on 57 percent of his takedown attempts, but he still landed six and dominated the fight with his wrestling.

Even though Velasquez is not a particularly accurate takedown threat, he compensates with persistence. His career takedown accuracy is only 45 percent, but he attempts 11.2 takedowns per 15 minutes. That number of attempts allows him to land 5.15 takedowns per 15 minutes.

Since the Miocic fight, Ngannou has stopped all four of the takedown attempts against him and shown improvement in terms of takedown defense. In his first fight against Curtis Blaydes, Ngannou allowed Blaydes to land two of his six takedowns. In the rematch, Ngannou stopped both of Blaydes' attempts and finished the fight in the first round. Blaydes leads all ranked heavyweights in terms of takedowns per 15 minutes with 6.75. The fact remains, if Velasquez can keep his usual takedown pace, it likely will mean trouble for Ngannou.

Fight time

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Velasquez and Ngannou average virtually the same fight time per bout. Entering the fight, Velasquez's average fight time is 7:17 and Ngannou's is 7.16. However, it certainly seems like a longer fight favors the former champion. Ngannou has fought past the second round only twice in the UFC and lost both times. On top of that, "The Predator" fades harder after the opening round compared to Velasquez.

It is natural for a fighter to experience a decline in activity after the first round. In the opening rounds of his UFC fights, Ngannou has landed 2.91 significant strikes per minute. Following the first round, his rate falls to 1.29, which is a 56 percent decline. Not only does Velasquez historically have a higher striking pace in opening rounds, but he also has experienced less of a decline by percentage. In his opening rounds, he has landed 8.13 significant strikes per minute. That rate falls to 4.67 over the following rounds. That rate is still well ahead of Ngannou and represents only a 43 percent decline in striking activity.

The longer the fight goes without a finish, the more likely it is that Velasquez will walk out with the victory. Ngannou should enter the cage with a strategy based on getting to Velasquez early and finishing the fight.