Looking at the pacers they seem to have three serious issues. First is that they get very stagnant on offense and don't move the ball. This is because they don't have many real scoring threats or natural distributors. Paul George isn't quite ready yet, and he isn't the passer at small forward that Granger at his peak was, which means teams can concentrate on him more. Hibbert is streaky and prone to disappearing on offense and on the glass. Stevenson is J.R. Smith but more willing to play defense and with a bit less talent on offense. Hill is a good defender, but merely a competent ball-handler and a bit lacking in court vision for a point guard. He can put up pretty decent numbers on offense when there is ball movement, but when there isn't going to be the one to create points or start breaking down the defense.
West is getting older and less mobile, which being slightly undersized for his position hurts him more than for a bigger PF, it also means his playing closer in to the basket, which doesn't help him as a distributor, and can make it harder to get a pass to him.
Also since they only have one player who is really able to be counted on as an offensive first option, in George, at least 2 of the group of West, Hibbert, Stevenson, and Hill have to be having a decent night on offense for them to win. Otherwise all the defense in the world can't beat an above average team.
Their second issue is no true leader, George really needed another year before he would have been ready for the roll. West doesn't have the personality for it and neither does Vogal. Hill has the personality but can't do it as an only moderately talented fairly young player. Hibbert might be able to but hasn't stepped up. Bird definitely can't do it from the GM spot even though he has made a few attempts.
Finally their final issue is panic, though it is partially related to the first two. This is a team that depends on team scoring and ball movement for their offense, that sort of team, can't panic and fall into pointing fingers, it definitely can't go into isolation scoring mode to try and get their points.