PSU is quietly playing really high level defense. Even if they give up some offensive rebounds and aren't the most athletic team, as a unit they rotate and really work to not give up easy shots.
They played excellent defense throughout the B1G tournament. That's been a big area of improvement/growth during the season. I actually read one "analysis" early this week (a couple of sentences on each team) that actually said that PSU was weak on defense - boy was that 'analyst' in for a surprise.