He is a 2019 guy who committed almost 2 years ago now (summer of 2016). But now the likes of Alabama have shown interest in him.
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Another factor may be that 2 of the 4 coaches that he mentions in his decommit tweet (Coach Mahe and Coach Ofahengaue) are no longer with the program. It makes for the perfect storm for him to spend the next year being courted by some of the country's biggest programs. If you look at what the kid says, he committed at age 15--now a couple years later things don't look quite the same as they did back then.
I'd rather see him spend some time now figuring out what he really wants to do (what school to attend, is a mission in his future, etc.) than have him back out last minute or flip when signing day rolls around. If he is going to decommit, you know that means he is probably leaning towards other programs. I'm trying to think of a decommit who changed their mind and stuck with BYU in the end but am coming up blank.