Average Score Competitions allow players to compete on their average score, rather than specific metrics. This means each user's score is determined by the sum of the amount field on the events that apply to their score divided by the total number of events.
For example, if a player in a Deals Won competition has 3 deals that count towards their score, one worth $10,000, another worth $20,000, a a third worth $30,000, then their score on an average score leaderboard would be $20,000: ($10,000 + $20,000 + $30,000) / 3 deals = $20,000
A team competition works in a very similar way. If there are 3 deals that belong to any of a team's members all will apply toward the whole teams' score, then the team's average score is the sum of the deal values divided by 3.
Here's how to set one up:
If you don't know how to set up a Competition yet, see: this article first.
When you create your competition, select the "Average" competition type. Average competitions will give you the option to set up an average target, and then automatically convert your scores into averages.
Next, set up your goal metrics and targets. If you are looking to strive for a particular average target, make sure to add the number in the target field: 
Then just finish creating your competition as normal and you're good to go!