The fielder has to have the ball in his possession but if he drops it he doesn't have to tag up.
Actually, the fielder doe NOT have to have possession of the ball for a base runner to tag up and advance. Once the runner is on the base ("tagging up") he may advance as soon as the fielder touches the ball, whether he has possession or not. In other words, the base runner may advance even if the fielder is bobbling the ball and then catches it, i. e. has possession.
I assume the question means the fielder is on the ground (floor?)..in either case, the fielder legally tagged the base while holding the ball firmly and the batter is out. See definition of "tag" in baseball rules. It is the same as the firstbaseman touching (tagging) first with his foot while the ball is in his glove. This would not be true if the runner is not forced, in which case the fielder must tag the runner with the ball held firmly in his hand or glove.
No.
To prevent collisions between runner and fielder
I will assume you mean when a batter has hit a ground ball to an infielder and the throw to first pulls the first baseman off the bag. On any force play, and the above would be considered a force play since the batter is forced to run when (s)he hits the ball, the batter would be called out because it is only necessary to have full possession of the ball and touch the base before the runner does.
Yes. For example, runner on 2nd, batter hits ground ball to the shortstop, who, instead of throwing to first, throws to third base in an attempt to get the runner. The batter is charged with reaching first on a fielder's choice, even if the runner is safe or out.
It's a judgment call. I think the answer is this: A play is scored as a fielder's choice if, in the official scorer's judgment, the fielder had a clear opportunity to throw the batter/runner out at first, but instead chose to putout another baserunner. So I suppose a batted ball is scored as a force out if the fielder has no realistic chance (in the scorer's eyes) to get the batter/runner out at first and his only choice is to tag another runner or throw to another base.
Yes runner is out (unless the ball has already gone by a fielder other than the pitcher), the ball is dead and the batter/runner gets first base.Correction:It is not relevant as if the ball goes past the fielders (only if it touches a fielder first) -- any time a batted ball first hits a runner in fair territory without touching a fielder first -- the runner is out, the putout goes to the nearest fielder, and the batter is still credited with a single and gets 1st baseCorrection to the correction:It does matter if it goes past the fielder first. This is infielders other than the pitcher and catcher. Because the fielders have had the opportunity to make a play on the ball, the ball is no longer dead. The batter would then advance to first at their own risk and the other runners would advance at their own risk too.
Yes, but if I were you, I wouldn't try it. Though you can if you want.
The hitter is a slow runner.
he is out
The runner is probably out for interference by running into a fielder, if not, he is out if the throw to first beat the runner and the first baseman, or whom ever is covering first, had his foot on the bag when he received the ball.
That would be considered a fielder's choice. Answers.com defines a fielder's choice as: "A play made on a ground ball in which the fielder chooses to put out an advancing base runner, thus allowing the batter to reach first base safely." Even though, in your question, the runner was not put out at home the play would be scored a fielder's choice and the batter would be credited with an RBI.