Question: What is the objective of the defensive chop?
About the article "Table tennis", section "Chop".

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A chop is the defensive, backspin counterpart to the offensive loop drive.
A chop is essentially a bigger, heavier push, taken well back from the table.
The racket face points primarily horizontally, perhaps a little bit upward, and the direction of the stroke is straight down.
The object of a defensive chop is to match the topspin of the opponent's shot with backspin.
A good chop will float nearly horizontally back to the table, in some cases having so much backspin that the ball actually "rises".
Such a chop can be "extremely" difficult to return due to its enormous amount of backspin.
Some defensive players can also impart no-spin or sidespin variations of the chop.
Chop Chop may refer to: chop chop (phrase), equivalent to "hurry" or "do it quickly" Chop chop (tobacco), Australian English for homegrown tobacco Chop Chop (song), the second single by rap group YoungBloodZ Chop Chop (band), an electropop band out of Los Angeles Chop Chop (horse) (1940–1963), Canadian Horse Racing Hall of Fame racehorse "Chop Chop" (Bell X1 album), 2013 "Chop Chop" (The Academy Is... album), the working title of the album "Santi" Chop Chop, Iran, a village in Zanjan Province, Iran Chopper Read (born 1954), nickname used when referring to himself (particularly 'Uncle Chop Chop') A character in the "Blackhawk" comic book series "Chop-Chop", a 1982 single by British post-punk band Killing Joke The title of Shwa Losben's 2008 indie rock album An Undead character in "" DeMarcus "Chop Chop" Corley (born June 3, 1974), is a boxer from Washington D.C., and a former WBO and USBA light welterweight champion.
current NABF Light Welterweight champion.  
Chop chop, also known as loose tobacco, is an Australian term for untaxed, cheap, illegal tobacco, such as that which is home grown.
"Chop chop" avoids heavy excise and taxation levies and can be much cheaper than the legal product.
The "chop chop" industry is illegal and unregulated. 
A pork chop bun is one of the most famous and popular snacks in Macau.
The bun (piggy bun) is extremely crisp outside and very soft inside.
A freshly fried pork chop is filled into the bun horizontally.
Macau pork chop buns are made to order.
The ingredients of a pork chop bun are only a piece of pork chop and a bun without additional ingredients like lettuce or cucumber. 
In gridiron football, a chop block is an attempt by an offensive player to cut block (block at the thigh level or lower) a defensive player who is being blocked above the waist by another offensive player.
In the National Football League (NFL), a chop block is legal on running plays when (i) the blockers are aligned next to each other on the line of scrimmage, (ii) the blockers were lined up anywhere on the line and the flow of the play is towards the block or (iii) the cut blocker was aligned in the backfield and the chop block took place outside the original tight end position.
The cut blocker is said to "chop" the defender and usually engages simultaneously with or immediately after the high block.
A "reverse chop" occurs when the high block comes immediately after the low block and the same rules apply.
In the NFL, college and high school football, the penalty for an illegal chop block is 15 yards.
They were first banned in the NCAA in 1980.
Chops block are illegal in the NFL on passing and kicking plays, as well on any play with attempted pass blocking or kick protection but which are actually running plays.
It is also an illegal chop block if a player "lures" a defender by "pass-blocking posture" while another player chops him.
The continued legality of chop blocking, as of all low blocks, is controversial.
Partisans of the offensive line see it as a traditional run blocking technique, while those of the defensive line see it as unnecessarily dangerous.
In the Canadian Football League (CFL), chop blocking is defined as cut blocking a player already engaged, physically or otherwise, with another blocker.
It is always illegal and carries a 15 yard penalty.