Arrows have 2 importants points to understand-
1-Visual displaying of players.As each one of the 5 mentalities that change the pressure line, the arrows change the player move.

2- % added the the internal base of attack/defense player contribution.
A Defendive MC, always, always, will help in defense if theres option (this means there's a chance, as "defensive player "by defult", to be selected as the player that in the visual action defend) despite that you can add him a red arrow.
"
So let's separate, attacking actions and defensive actions -(these always exist, Hard defending mentality, can be full of attack actions, and viceversa)
Then is a matter, of Internal ratios, and "random selection" that depend of each match, to explain it simplifyed, and all don't depend of what we see.
A 1% speed player, can win all actions in a match vs a 200% (uhh^^)
A FK specialist, can miss every match.
(well I could mention all SAs here abd its superawesome evidentialistic effect lol)
And a long etc of things that, often we discuss here, so, a "arrow" don't mean that a action will have success at it's 100%, cause this depend, of the own calibrations of contributions that the game does in our team.

Of course there's a move of power from a line to another (successful or not) that "can" (or can not) be determinant to affect the balance in our favour, giving us more/less control.

And more or less I think it's this. xD