I'm guessing then, that you have no clue about the family background of Ryder.
Abandoned by his parents, raised by a single grand parent, moved around quite a bit and the only reason he ever had to be confident about himself was his sporting ability.
The whole overweight thing? Yeah, probably a case of insecurities feeding a tendency to be an emotional over-eater.
The whole drinking thing? Textbook abandonment issues.
Constantly ****ing up when in the spotlight? Abandonment issues, depression and insecurity.
Now realise he grew up in a poor area, amongst a bunch of friends who are social misfits and underachievers, who see getting **** faced as the in thing to do (welcome to New Zealand, binge drinking is prevalent throughout society, any club cricketer will tell you there are several "Jesses" in every single club, just not with the same degree of talent). His support structures that he goes to when he's had bad news or is feeling bad are a bunch of young mates who all console him by doing what young males in NZ do - getting ****faced, then he goes out, and his abandonment and insecurity issues make him act out because he wants attention.
I've never even studied psychology but to me - the above is pretty evident as to why he acts out and it's a case of not being managed well. The same case exists amongst a LOT of sports stars in New Zealand - Zac Guildford is a prominent one, Cory Jane is another, the constant issues Maa Nonu had during his youth. The difference? Rugby doesn't tend to piss all over someone in this case, they also have better support structures in place.