change his bad mechanics. In baseball, many of the all time great hitters had to do more than practice, they had to resist those who tried to change their alleged bad mechanics.
And i knew a great prospect whose talent declined because a well meaning expert coerced change.
Sometimes changing mechanics is the right thing to do, sometimes it's insane. When someone is hitting as consistently as Leifson, it's smart to leave his mechanics alone.
FWIW, JMHO.