Tag combos are taught to you in the fifth Combot stage. If you aren't feeling like playing through these just yet, I'll explain how to do them below using the combot character.
First, you must launch your opponent in the air. This is down by pressing towards them + Y on default controls. Immediately after doing this switch out to your partner using one of the bumpers, or clicking the right stick. Landing an attack while the opponent is still in the air will count once towards the achievement. Do this ten times to unlock.
Personally net myself all of these while going for the combot challenge, however you will also be able to do them in standard combat rather easily as well. Must be done in tag, if that wasn't so clear.