Defense in MC is a slightly different animal than on other modes.
Defense on your assigned man is not always appropriate ... look for your matchup and stick with him, even if the coach says to cover another. An example here: In my last game, I was mainly assigned to Lin but every once in a while on a "transition" my assignment would be called on Sacre. I ignored that assignment and stayed with Lin. This prevented the inevitable kick-out to exploit the open 3 ... Yes, Sacre would score a time or two because my bigs were delayed in rotating back - a two point bucket is better to give up than a three.
General tip 1: Use spacing to "assist" your teammates more than actual rotation. What I mean by this is the ai recognizes a circle around it as a zone of containment and if your ai teammates are not closing properly or shading the nest, you can sometimes enter their "zone of awareness" to force the proper movement.
Example: I was assigned to Lin and Ginoble was assigned to Kobe. The Lakers run a horns type of play right leaving Kobe shading towards left base and Lin at the left arc position. Normally, Lin would then kick it to Kobe who then would do his thing and score more often than not because Ginoble was not up in Kobe's grill enough. Using the ai spacing mechanism you can shade yourself to be in Ginoble's "area" forcing him to move closer to Kobe and preventing said scenario. It is very important to get back tight on Lin once you trigger this movement because your goal is not to trigger a switch or a rotation, only to get some extra closure needed to trigger the "contesting" of Kobe's isolation.
General Tip 2: When the opposite team is running a baseboard drive you can assist your ai teammate in stifling the drive at two main points: the very beginning and at the rim. Any other point on the arc and it will result in a shooting foul or a posteriser.
If you are in position to help immediately, your goal is to trigger the ai's "swarmed" animation where the offensive player thinks you have him double-teamed. It is important not to double team but only trigger the awareness of the ai - this will force the offensive player to "pull up" on the drive sequence and then look for an outlet. This is why you do not double team but rather get back to your assignment to cover the outlet. Your ai defensive teammate will then be able to cut any baseboard movement.
If you are not able to assist your teammate immediately then your only hope of defending this drive is to become a hawk on the block. Even as a PG, you can often come from behind and time everything correctly to block the attacker's shot. Especial;ly as you learn the individual's animations for layups and dunks. I had 4 blocks on Dwight Howard as a PG because of the hitch in his animation allowing me to strip him on standing layups.
If you want more tips or clarification, let me know.