Why is tennis scored so oddly?
For those not in the know, tennis is scored 15, 30, 40 rather than the more traditional 1 point, 2 points, 3 points of other sports. This is because in its early days as an indoor sport, a tennis game's score was kept by moving the hands of a clock to 15, 30 and 45. Later, for reasons now rather obscure, the 45 became 40.

WHY IS A ZERO SCORE IN TENNIS CALLED "LOVE"?
When tennis first became popular in France, a round zero on the tennis scoreboard looked something like an egg and was therefore CALLED an egg. The word for egg in French is "l'oeuf". When transferred to America, "l'oeuf" was pronounced "love".

Why do tennis balls feel fuzzy?
Tennis balls aren't completely bald for two reasons. The fuzz is there, for one thing, to slow it down. You might find that hard to believe had you ever had to receive a cannonball serve from John McEnroe, but there you are. It facilitates rallies by increasing wind resistance and preventing the ball from leaving the stadium on one bounce.   The fuzz also increases racket control by holding the ball against the strings for just a fraction of a second longer than would happen with a smooth ball.
As for me, I visit the bar in the clubhouse before the match. After that it's not just the balls that are fuzzy.   Source: JUST CURIOUS JEEVES by Jack Mingo and Erin Barrett

Catgut
Is the "catgut" used in some tennis rackets and stringed instruments actually...?
These days tennis rackets tend to be strung with steel or nylon, but some are still made from sheepgut, which is known for its strength. And when you strum a guitar, don't be surprised if you think you hear a bleat among the twangs.   Sheepgut is still a mainstay in string instruments. It also shows up in surgical sutures and--don't faint--sausage casings.  So why do they call it catgut? Fewer letters? Because sadism toward pussycats is politically correct? In truth, we don't  know.   (Source: HOW DO THEY DO THAT? by Caroline Sutton)