Scoreboard with score evolution plots using classes
I think your use of classes mostly makes sense. 

The key to object oriented programming, in my humble opinion, is relating how we think about objects in the real world to the way our code is structured. If you were playing a game, would you, as the player, add a score to the score board? Well, it might depend on the game. Sometimes, the game might determine your score and add it to the scoreboard (I'm thinking battleship). In that game, the player doesn't add their score to the scoreboard, it is behind the scenes in a way. 

I like that you created a class player, most games revolve around players and encapsulating that information in a class makes sense. 

When you play a game, does the scoreboard determine when a new round occurs? Not really, that is sort of inherent to the game. The scoreboard, which in the real world encapsulates information needed just for displaying information related to a game, doesn't actually make decisions about a game. It merely receives information and then displays it. Therefore, it might make sense to separate your scoreboard's display functionality from the functionality of actually playing the game. 

This could happen by creating another class called game that would have as members of the class player's and a scoreboard. The game class could be responsible for starting a new round and be responsible for making sure the scoreboard is updated and the player's own score is updated.

Often in OOP, methods are like actions and take on verb-like names. I like that you called your method add_score inside player.

I hope this is constructive feedback and you find it helpful. If you have any questions, let me know.