I found several very bouncy blueish balls. I put a hole in one and a
milky white substance oozed out. They were found under 2 trees in a
park where golfers practice. Any idea what they might be.

pear..

Thanks for your question.  While Journalist may be correct with her
AGB theory, the chances are better that what you found were the cores
to golf balls.  Golf balls, years ago, were made by taking either a
liquid filled core (which you found) or a solid rubber core, and that
core was wrapped tightly with a wound layer and the outer covering was
then put over it.  This was known as three-piece construction.  Two
piece balls are the same concept except the core is much larger and
there is no wound, middle layer.  The key difference is that a
two-piece ball tends to travel further, while three-piece balls are
easieer to control. Liquid cores help regulate the ball's spin.
Three-piece balls in typcially have high rates of backspin. High
backspin = more lift = ball stays in the air longer. It also makes the
ball stop faster when it hits the ground. Liquid centers also provide
a softer feel when one hits the ball.  The liquid is typcially a
mixture of water and corn-syrup.

Thanks for your question and if you found several of the balls in the
out of bounds area, chances are they were mine at one time!

If you need any additional clarification, please let me know prior to
rating my answer.

Regards,

-THV

Search Strategy:
golf ball core liquid

References:
Does the center of a golf ball contain a deadly poison?
http://www.straightdope.com/classics/a5_168.html

Ball FAQ
http://hkprogolf.com/ball_core.htm

Asphyxsiated golf balls are frequently mistaken objects found in
nature.  When the ball's soul leaves the casing after having all
career shots strangled away, the ensuing decay closely resembles what
you describe.  (Golf ball death can also be caused by too many hooks
or dog leg lefts.)

Whatever you do, *don't* allow any of the decaying matter to touch
your clubs.  If it does, rinse immediately with the alcohol available
at the 19th hole: the acidic properties of the decay cause
imperceptible indentations in the face and head of clubs which results
in the club whistling when thrown, thus alerting all other golfers on
the course that you have a short fuse.

Hope this helps.