Yu Fei wanted to exploit Red's mismatch, but that was not easy.
Because avoiding Yu Fei's mismatch was part of The Celtics' game plan. As long as Yu Fei called for a pick-and-roll, Red would not switch or help on defense; the only person he needed to keep an eye on was Roy. If Roy went to set a screen for Yu Fei, he would double-team Yu Fei if necessary, but he would not switch.
This meant that Yu Fei could not target Red right away.
Meanwhile, The Celtics' offense showed signs of revival under Cassell's control. Cassell, unlike the young Rondo, was well aware that even though the team had an advantage in the paint, the offense would struggle if every player wasn't firing on all cylinders.
However, what The Celtics didn't expect was that their most reliable player in the paint began to have issues.