Real wrestling is hard. It's a good martial art/grappling sport to know too, as it's the transition between stand-up and ground grappling. Most Brazilian jiujitsu black belts have a near impossible time submitting a solid wrestler off of their back as wrestlers have such a good base.
5/7 current UFC champions have a wrestling base or
very strong wrestling.
Justin said:
Boxing is the most challenging sport.
Mixed martial arts would be the most challenging sport. But I mean when you've got some asshole in the ring trying to rip your arm out of its socket or turn your face into a pothole, you can hardly consider it a sport.