Win-Loss Record in SQL Server
I would start by determining the stats at run-time. Only if that turns out to be too expensive, I would denormalize the statistics:

select f1.fighter_id
     , count(case when f2.is_draw = 0 and f1.fighter_id = f2.winnner_id then 1 end) as #wins
     , count(case when f2.is_draw = 0 and f1.fighter_id = f2.looser_id then 1 end) as #loss
     , count(case when f2.is_draw = 1 and f1.fighter_id in (f2.winner_id, f2.looser_id) then 1 end) as #draws
     , ...   
from fighter f1
join fights  f2
    on f1.fighter_id in (f2.winnner_id, f2.looser_id)
group by f1.fighter_id;