Everton boss Rafa Benitez was unhappy with home fans for jeering Salomon Rondon during defeat to Brighton.
Sections of the Goodison Park crowd booed when Rondon was being readied to come on during the second-half when Everton were 3-1 down.
Rondon then coming on to replace Jonjoe Kenny prompted more boos and Benitez, who has seen other substitutions met with an angry reaction, was at a loss as to why some fans booed.
"It is difficult to understand," he said.
"You take off a defender and put on a defender when you are losing. normally people are happy with that and, hopefully, can understand that we are trying to do the best for the team."