If one looks really closely at Sandoval's defensive WAR one sees that his defensive ability he never has been outstanding "From 2009-14, he ranked ninth out of 19 qualified third basemen in Fangraphs' Defense metric (19.7) and 10th in Ultimate Zone Rating (8.7). So he was right in the middle of the pack — pretty good. " but not outstanding
"Then came 2015, his first season with the Boston Red Sox. His Defense metric (-15.1) and UZR (-16.9) ranked worst among all qualified third basemen. "
More importantly in 2014 he lost 40 lbs in 2013 he lost 22 lbs. Photos of him in 2014 show a much slimmer man. So the obvious conclusion is that Sandoval has to lose a lot of weight in order to be an effective above average fielder. In 2014, he was motivated by his upcoming free agency, what motivates him now?