Sports Science: Dive vs Run
With the first baseman's foot on the bag, this would not
be the correct time to dive into first base.
When a runner is flying down the line and really needs to be safe, sometimes the competitive nature comes out and the runner just does it. He doesn't even think about it beforehand. He just dives for the bag. I just think of the olympics. If diving worked, every sprinter in the olympics would dive at the finish line. None do which tells me it must not help a runner. Otherwise, they would do it.
To avoid a tag, diving into first base would be justified.So does that mean a runner should never dive into first base? No. There are times when it is a smart move by the runner. Such a play occurs when a first baseman comes off the bag and tries to catch an errant throw and then apply a tag for the out. To avoid this, here's what the runner focusses on as he runs down to first base. He pays attention to the first baseman's feet as he runs. If he sees the first baseman's feet leave the bag in order to get a throw that seems to be wide on the home plate side of the bag, the runner can try to slide or dive making it harder for the first baseman to tag him. If the first baseman's feet are on the bag, the runner just continues to run through first base as normal.
Of course, in many instances, the timing of the play will not give the runner much time, if any, to recognize what's happening and decide to slide. It should also be noted that many finger, wrist, and shoulder injuries occur when runners dive into first base so it should only be used when completely necessary.