I doubt that the deceased had a lot of expertise or experience using a bat as a weapon, and the results showed it. If I had to guess, I'll bet that he took a swing at the intruder who ducked and stabbed him.
A bat can be a devastating weapon, but like any weapon, it has its limitations.
It's only really powerful about halfway through the swing. Caught early, it hasn't yet had time to build up the speed necessary to translate its mass into damage. Too late, and the user is trying to slow the swing down instead of swinging through the intended target. It's also got a tendency to glance off whatever it impacts. Not to mention that the ones I used even in little league were 28"-32" long, making it rather ungainly unless you use it inefficiently as a thrusting weapon.
In other words, even if you managed to connect with the thing, there's a very good chance that the strike would be ineffectual for whatever reason.
Coincidentally, good to read up on what kinds of injuries can be inflicted by various improvised weapons. Goes to the "reasonable person" standard should you ever stand trial. One such picture got shown to a group of medical examiners in training. It showed a fairly large man, who would have been over 6' 6", if he still had a head. Suffice to say, there was a fair amount of gore, but nothing that could be identified as once having been a human head. The instructor asked the students what weapon they thought had inflicted that damage.
Most guessed a shotgun. A few thought it was some kind of machinery accident. Several thought explosives, including one guess of "hand grenade".
It was a standard, household hammer, wielded by the deceased's battered wife. She stood, IIRC, 5'4". Got tired of being slapped around, grabbed the hammer, and when he didn't take her seriously, cracked him square in the skull with it. Once he was down, she just kept going until she decided she was finished.
