We don't need any intro, you all know him. John Diggle, aka Black Driver, aka Spartan, aka the man with the worlds largest arms.
Due to Diggle's experience in the army, he has great knowledge on most firearms, reigning from handguns to grenade launcher. Diggle most often sports his trusted handgun that fires tranq ammo. A common misconception is that Diggle always kills the criminals he goes up against, even though he has on a number of times stated that he uses tranq ammo. Even though Diggle most often uses tranq ammo, he has no problem killing, and has killed on many occasions.
Diggle's handgun can also shoot grapple rope.
The rope is strong enough to hold enhanced Derek Sampson.
Diggle goes on a one man mission to Kasnia to rescue the Human Target. He comes down as a paratrooper, and takes out an whole army by himself, utilizing his assault rifle, a grenade launcher, a handgun and his knife. If this doesn't earn the Black Driver some respect, I don't know what does. One man army.
Diggle was already before his training with Oliver a very capable fighter, mostly due to his time in the army, but also as his experience as a body guard.
Diggle has been trained by Oliver in multiple forms of martial arts.
Diggle is able to hold out longer than both Thea and Laurel in a training session with Oliver, Digg proves himself quite a challenge for Ollie it seems. It's very evident how drastically Diggle has improved during his years with Oliver when comparing their training sessions.
Diggle's h2h skill often goes unrecognized, his skill is very evident in his fight against the Shadowspire mercenaries. Notice how all of Diggle's punches are extremely well placed.
Digg is able to put up a decent fight against China White, as of season 2
Diggle is easily able to beat Ghosts in close quarters combat. At times he is fighting multiple Ghsots simultaneously.
Diggle has also proven himself against skilled opponents, such as the League ninjas. Against Talia's section of the League:
Diggle is skilled enough to go toe to toe with Dominators
Diggle has also been able to fight on par with and beat Black Siren. Diggle had the clear upper hand in both fights.
He is skilled enough to hold of Ricard Diaz in a shorter period of time. Diggle even gets in a couple of half decent hits as well, and is by no means out matched.
This fight needs some context to it. This is not a fight for the combatant to showcase their skill, nor is this a fight that showcases their true abilities. This is a rage filled brawl between two brothers, and Diggle does really well to trade blows with Oliver the way he does. This is a very impressive showing, although I do not interpret this as Ollie and Digg being equals.
Due to his training with Oliver and his military training, Diggle is in peak physical condition.
In ep 1x22, when Digg dresses up as the Hood to interrogate Moira, Diggle beats Oliver to the point where Oliver is limping and his face is completely swollen, this was when Digg was pulling his punches.
In ep 1x12 (25:05), Diggle overpowers Oliver, pinning him to a table.
In the next gif, Digg reacts to bullets being shot from behind, moving out of the way and at the same time pulling his gun and returning fire at an insane speed. Andy even comments on his speed:
You still got those quick reflexes, JohnAndy Diggle
Diggle tanks a canary cry in episode 6x14
His reinforced kevlar allows him to tank bullets straight to the chest
Diggle's convoy in Afghanistan is attacked by Taliban troops, the troop consist of over a dozen men. The Taliban kills all of Digg's men and then stabs Dig in the back with a hatchet. Dig proceeds to rip the hatchet out of his back and kill all of the Taliban himself, Digg managed to kill them all before a scarf could hit the ground. An excellent showing of speed, endurance and his combat ability.