Via ESPN Insider:

So, in order to qualify for this list, a player needed to have played at least 10 minutes per contest over the course of at least 100 career games with the franchise. Furthermore, we've added the "Bruce Bowen Corollary" to exempt players who started for championship teams.

Here's the bottom 5 Haberstroh came up with for the Sixers:

Bob Thornton ('88-'90)

Danny Vranes ('87-'88)

Jayson Williams ('91-'92)

Bob Harrison ('57-'58)

Manute Bol ('91-'94)

Fortunately I'm not old enough to have witnessed these guys in their anti-primes, but one guy who I have had the displeasure of watching for what seems like decades -- Willie Green -- just missed the cut. The fifth guy on Haberstroh's list was Manute Bol who had a PER of 8.2 from '91-'94. From '04-'07 Green's collective PER was 9.6, but he also accumulated a disgusting -0.7 win shares during that stretch. Bol contributed 1.1 during his three years of stank, so if I ever made a list of worst Sixers ever, Billy Green's spot would be guaranteed.