A baseball swing produces long fly balls? wow.
On the opposite end of the spectrum, what are the best drills to help fly ball hitters (not pop ups) hit more line drives?
Are you 100% certain of this?
Guess I should have said "typically the barrel is going to be on a upward angle". It doesn't have to be.
Statistically a rising line drive can be hit by swinging straight down if the bat strikes ball at precisely the right time and location. Of course this would only put the bat and ball on plane for a fraction of a second and greatly reduce the amount of barrel surface that passes through the ball's plane. With gravity acting on every pitch the instant it leaves a pitchers hand an upward angle in barrel swing (degree varied by ball plane location) will put the barrel on plane for a longer period of time exponentially increasing the chances of contact, and as contact chance increases so does chance of contact point producing rising line drive.
The ball is round, the bat is round. Both of those factors can either add or subtract loft. Swinging up while hitting the ball above the center of it's equator will produce a humpback liner or ground ball. That's just a couple of possibilities. You can swing up and hit just slightly below the equator. You can swing level and hit above or below the equator. You can swing down and hit slightly above or below the equator
See if this makes sense:
I just added other possible ways of hitting a line drive. Yes, what you say is the general ideal and what a hitters is looking to do. There are other possible was of achieving a line drive less than ideal. My DD's goal is to hit line drives and yes we 'try' to hit on a slightly upward barrel angle.To achieve the rising line drive the barrel is typically going to have to be traveling on an upward angle matching the plane of ball.