YOU imagine only kryptonite would have this effect, but Sonny Bill Williams admits his latest sporting challenge is both ''daunting and scary''.
Having played elite rugby and league, boxing has until now been something he dabbled in, albeit successfully in a fistful of fights against hardly elite opponents. But it gets a little more serious on February 8, when he fights Richard Tutaki for the New Zealand heavyweight title.
''Obviously I have my critics no matter what I choose to do but at the end of the day it's a fight for a title and it's a big fight and he's had 40 fights and this is my fifth,'' Williams said yesterday. ''People wanted me to step up. This is definitely stepping it up.
''It's a big risk but I thrive on taking chances and seeing where I'm at. This is no different and it's pretty daunting and scary - I won't lie - but I'm enjoying it right now.
''What would the title mean to me? I don't think I'd really appreciate it until I've finished. In saying that, being able to say that I was a New Zealand heavyweight champion at one stage, that would be pretty cool.''
Williams says his preparation for the fight is going well, particularly as most of his focus is on boxing training, not split between rugby training, and he's learning new things every day. While a New Zealand title would be ''cool'' so too would the match everyone wants to see against Barry Hall.
''Down the track anything is possible,'' he said. ''But obviously for me, I try and take everything as it comes. At this stage I'm fighting for the New Zealand title against Richard Tutaki. You never say no to any opportunity but we'll just see. At this stage it's about taking small steps and I haven't had any amateur experience or anything like that. I'm just looking to learn my craft and get the best kind of training I can and get more confidence. It's about me and doing what is best at this stage for my boxing career and trying to test myself.''
Two weeks after his title bout, Williams will start the Super Rugby season with a new team, having moved from the Crusaders to the Chiefs. He moved to be closer to his mother, who lives in Auckland, and most expected he would head to the perennial contenders the Blues instead of the Chiefs, the lowest-ranked Kiwi Super Rugby team last season.
He says he likes a challenge and is motivated by the one offered in Hamilton. ''A lot of things I do are to try and bring the best out in me. I like to put myself in hard situations where I know I have to bust my arse and work really hard to get the best.''
Another factor of his move was his close relationship with All Blacks assistant Wayne Smith who has taken the job of technical adviser with the Chiefs. Williams credits Smith with having faith in his ability and that he could become an All Black. He did, and played in the World Cup.
''Obviously I didn't play much game time in the semi-final and the final but I believe I didn't let myself down. Every time I put the black jersey on in the World Cup I played well, and for myself that is a big thing because I'm my harshest critic.''
This could be Williams's final season of Super Rugby. He signed with the New Zealand Rugby Union for just one year, and in 2013 is eligible to return to the NRL as part of his departure agreement with Canterbury.
He said he had ''no thoughts about that yet'', but understands already the doubters are out there about a comeback to league.
''Whatever I do people seem to think I can't do it,'' he said. ''People will always have their opinions but what matters to me is what I see when I look in the mirror and how my family look at me.
''I wouldn't say I don't care what the perception of me is and what other people think. But I value the opinions of people that I hold close to me. When I walk the streets I always get mad respect. As long as I keep getting that, I'm sweet.''