Per Basketball-Reference, Gordon Hayward played 70% of his playing time at small forward for the Jazz in 2016-2017. For the Celtics, he started at the 4 on that fateful night in Cleveland. With Kyrie Irving firmly at the point and Al Horford manning the 5, Hayward is the obvious choice to be the de facto power forward.
To some extent, it really doesn’t matter how we categorize Hayward’s position. Particularly with the starting lineup, the parts are so interchangeable that traditional labels get thrown out the window.