Valuation discussion in a deal making scenario is a combination of multiple things. Some of which can be (not exhaustive)
1) Valuation Methods: DCF, comparable comps, precedent transactions, regressions of multiples v/s margins etc.
2) Broker Community Views: Analysis of the target price (or views) assigned by broker community tracking the company (for listed companies)
3) Industry Veterans: Views of senior folks, industry veterans or specialists who have spent some good time in the industry often are taken into consideration to add a premium or discount to a multiple depending on the situation
The football field chart is a graphical summarization of the valuation ranges that all the above methods yield
It can be thought of as a sanity tool which moderates the discussions of both the parties (buyer and seller) to maintain the valuation conformities in the deal making process.
A must know tool for all the investment banking enthusiasts and existing professionals