They have superhuman abilities in their suits, and the Ishina ninja use katana.
The Supah Ninjas(Mike, Owen, and Amy) use nunchucks, tonfa, and a staff most of the time.
Even then, they don't hit hard enough to hurt the rangers, who fight monsters on a daily basis.
Also, depending on the rangers, they have natural powers as well.
Like SPD, Red Ranger can phase, blue ranger has a force field, green ranger has psychokinesis, pink ranger has material mimicry, and yellow has multiplication.
There's a scene that comes to mind. Tommy is fighting his past selves. There's marble columns around. Green-Tommy kicks one of them at current Tommy as an attack. That takes tons of power.
Defensively, the suits also provide a lot of protection. Most attacks, guns and explosives, just cause sparks and knock them down but don't cause real injury. Even very major attacks just make them de-morph.
All of them can super-leap around too.
Some specific seasons have additional powers (sometimes even in civilian mode, like King mentioned).
And, while rare, conventional forces have been seen against the monsters, and they do pretty much squat. Normal weapons just aren't strong enough, while ranger weapons are.
Yeah, I know the girl on Supah Ninjas, and the sad thing is that none of the actors really know martial arts, while some of the Power Rangers are 7th degree black belts. So even outside of the shows, the Rangers will fvck the Ninjas up.
Tommy is played by Jason David Frank, who not only is a martial artist, not only has his own style that he teaches, but is also a legit MMA pro (5-0 record. Longest fight: 2 minutes. 3 of the 5 under 1 minute).
I've only watched 4 seasons in great detail but thanks to History of the Power Rangers, and to a less extent Dino Thunder, I'm familiar with most of them.
I've only seen four. Ninja Force, Dino Thunder, SPD, and Mystic Force. Each have there own advantages but it's between Dino Thunder and SPD for best to me. And I haven't seen all of the episodes for each season(except Dino Thunder and maybe Ninja Storm).