I am one of the developers of a very simple scoring app which you can find here: https://play.google.com/store/apps/details?id=nz.co.redblue.volleyball which might suit.
Some guys in Portugal are using it to do something similar in a stadium by using Andy Emulator on a computer attached to the screen and using an Android device to control it. You could also cast to the screen using a chrome cast or the build in Android casting if the screen supports it.
It's simply a web page that runs in an android web view so I could make it available online or send you the html file if that's easier.
It may also be with pointing out that if you want to listen to live commentary from your phone and keep up to date with the live timing screens you can download the brands hatch app which has a commentary live stream option and the official live timings board.
URL: https://play.google.com/store/apps/details?id=com.atzos.spyn&hl=en
Elevator Pitch: Majority of urban sports enthusiasts feel that they are not able to play their favorite sport as often as they want to. The main reasons are (a) lack of information about, and (b) inefficiency in connect with, players, coaches, clubs and activities nearby. spyn aspires to bridge these 'information' and 'connect' gaps.
More details: We have recently launched the app. We are a team of three co-founders
Looking for investment and hiring
I made an Android app, and here's a pdf. Keep in mind that this was from a year or two ago so with all of the construction you might have to modify a few holes.
I've heard good things from people using Harry's LapTimer. Haven't used it myself but it looks like it has good reviews. I believe it's possible to record 0-60 and the like. Keep in mind the Google Play Store does have 2 hour automatic refunds if you're hesitant on the price.
I'm new to darts, but I found this app last week: Let's Dart. I think it works well. Tracks player stats, is configurable for different types of games, and you can play against an AI, other people, or just solo.
The official app of the Detroit Lions has the option to listen to the radio play by play. Considering team sites and apps have to follow NFL guidelines, I would check out the official app for the Dolphins.
I just read the app description and it does have game day radio.