In
The Book, they've broken down bunt attempts with a man on first and 0 outs by early and late game situation, and the resulting win expectancy that a team would have should you bunt/hit away, basically the percent that a team will score in the inning following the bunt attempt. If the defense were playing as they were early in the game, you will win after attempting a bunt 71.6% percent of the time. If they were playing as they were in the 7th or 8th, you'll win 70.1% percent of the time. If it's the 9th, you'll win 69.6% of the time. If you swing away in the 9th, you'll win 71.5% of the time. So, clearly swinging away is better in most situations in the 9th, nothing else known about the skill of the hitter, the pitcher, the defense, etc. But, bunts occur in the 9th over 50% of the time in this situation, while early, they occur only 7% of the time. It makes sense that the defense would be playing in during the 9th and back before the 7th. Looking at the numbers, it's roughly equal to bunt early and swing late. However, if all you do is swing, then they'll stop playing you to bunt and it will be more like an early game situation where it is correct to bunt and incorrect to swing away, assuming you're playing for scoring a single run and not maximizing the total amount of runs scored. Therefore, sometimes you must bunt and sometimes you must swing away in order to keep the defense from playing optimally. Note that this is for only a man on first and not two men on, but I'd assume similar considerations apply.