Call the Play
Before a batter steps to the plate, try to predict the outcome of the at bat. For example, if you call strike out and the player strikes out, give yourself a point. If you predict a strike out and the batter does something other than strike out, deduct a point from your total. Keep track of the points throughout the course of the game, and the player with the most points at the end of the contest wins.
And, if you are really looking to get in depth, trying calling each pitch. Guess what the pitcher will throw, be it fastball, curveball, changeup, so on, and award points for the correct prediction.
Prior to the start of the game, go around the room and, depending on how many people are gathered to watch the game, conduct a quick draft from the pool of starting players on each team. Make sure the number of players selected by each participant is manageable, somewhere between three to five players. Then keep track of the outcome of each player's at bat over the course of the ballgame. The person whose team has accumulated the most hits by the end of the game, wins. You can expand the parameters of the game to include runs batted in, runs scored, extra base hits and/or stolen bases, depending on how in depth you want the competition to be. This will give all the viewers participating a vested interest and keep them involved in the game from start to finish.
And, don't forget the pitchers. Choose pitchers from each team and keep track of strike outs and award bonus points for selecting the winning pitcher or the relief pitcher who earns the save.
If you have Strat-O-Matic, the popular baseball-simulation board game, and player cards for the current season, play the game along with the actual contest. Fill out the lineups exactly how each team has penciled in their own for the game you are watching, and follow along with the action. See how your game compares to what's actually happening on the field.
Pick the Hero
In every baseball game, a deciding run will be scored. It could come in the top of the first inning or in the bottom of the ninth. But whatever run puts the eventual winning team ahead for good is considered the game-winning run. Choose through the list of participating players, and whoever selects the player who scores the decisive run in the game is declared the winner.
Home Run Derby
You can choose between the participating teams or draft your own team of three or five players from the two squads competing in the game you are viewing and have a home-run derby. Whichever team collects the most home runs over the course of the game is declared the winner.
Pass the Hat
Everyone watching the game puts a dollar into a hat at the start of an inning, and one person holds onto the hat when the inning begins. After each hitter completes his at bat, regardless of the outcome of the at bat, the hat is passed to the next person in a clockwise fashion. The person who is holding the hat when the last out is made to end the inning wins the pot.
This game can be adapted to use with other aspects of a game. You can keep passing it around until the first home run is hit, with each participant depositing another dollar into the hat at the top of every inning. Before the actual baseball game starts, have each participant write down on a piece of paper the combined number of runs he believes will be scored by the two teams playing, and the person closest to the actual number without going over will win the final pot at the end of the game, unless the game ends on a game-winning home run.