Intentionally mack on defense.

Hey - had a scenario at a tournament a while back, and thought I'd run it by you guys.
We were on defense, and the offense attempted a dump pass - my teammate read it perfectly, and got to the disc first. Instead of catching the disc or knocking it down, he deliberately macked it 15-20 yards upfield (where it landed untouched by anyone). Several players on the other team thought this was illegal, but could not explain WHY they thought so. Aside from potentially keeping the disc in the air long enough for one of the offense to recover it, is there anything actually wrong with this?
Also: If that is fine, what if he or a teammate were to then catch if after the mack? I'm assuming that is not allowed...
Daniel
We were on defense, and the offense attempted a dump pass - my teammate read it perfectly, and got to the disc first. Instead of catching the disc or knocking it down, he deliberately macked it 15-20 yards upfield (where it landed untouched by anyone). Several players on the other team thought this was illegal, but could not explain WHY they thought so. Aside from potentially keeping the disc in the air long enough for one of the offense to recover it, is there anything actually wrong with this?
Also: If that is fine, what if he or a teammate were to then catch if after the mack? I'm assuming that is not allowed...
Daniel