In my 5th grade, there was a period of time in which the 5th graders and 4th graders came together as one large group with the sole purpose of playing capture the flag on the full soccer field.
In this way, the offense could be considered as entrepreneurs starting out a business or a project of some sort. They're the ones that pitch ideas and then try to sell them to potential investors in hopes of obtaining huge success at equally high risk. Another thing they might do is attract people to their project so that it gains more support. The most important part of being the offense is never giving up.
In a business, the defense would be the people in charge of planning and scheduling, the seemingly trivial work but is in reality the most important of all. They would make sure everyone is running smoothly and doing what they're supposed to. Other tasks they might have are managing a website of some sort, or other social media websites.
In a business, these are your jack-of-all trades. They're there because they have many skills that can be used. They round out the different groups of people on a team and eliminate any glaring weaknesses. One day they could be helping creating spreadsheets, the next day they could be shooting a promotional video. Yet another day they could be just driving people around or making coffee. Their job is to make sure everyone else's job is running smoothly and nobody is overwhelmed.