(CNN) - Cases of self-defense aren't always simple -- especially in states with a "stand your ground" law.
Earlier this month, police say Michael Drejka fatally shot a man who shoved and knocked him to the ground in an argument over a parking space in Florida.
Although critics say Drejka's use of deadly force was uncalled for, the Pinellas County sheriff declined to arrest him, citing the state's "stand your ground" law, which gave him immunity. The decision sparked outcry and calls for reform.
But it's not the first time a "stand your ground" law has created controversy. Many states have similar laws on the books.
Here's what you need to know about them.
What is a 'stand your ground' law?
Generally, "stand your ground" laws allow people to respond to threats or force without fear of criminal prosecution.
Most self-defense laws state that a person under threat of physical injury has a "duty to retreat." If after retreating the threat continues, the person may respond with force.
"If you attack me in a non-'stand your ground' state, I've got to try to get out of it," explained CNN legal analyst Mark O'Mara. "I have to retreat before I attack ... The theory is, it (responding with force) has to be your last chance."
"But in 'stand your ground' states, you have no obligation to retreat," O'Mara said.
In other words, someone facing an imminent threat can use lethal force right away -- without first trying to escape.
How many states have 'stand your ground' laws?
While most states provide some form of legal protection in cases of self-defense, 25 have enacted "stand your ground" laws, according to the National Conference of State Legislatures (NCSL).
The laws in at least 10 of these states, mostly in the South, literally say that you can "stand [your] ground."
It's important to note that not all "stand your ground" laws are the same. States may word and even enforce them differently.
Why these laws make a lot of news in Florida
Florida has had several high-profile cases that sparked national conversation about "stand your ground" laws.
The state passed its "stand your ground" law in 2005, allowing people to meet "force with force" if they believe they're under threat of being harmed.
Of all the states with "stand your ground laws," Florida's is "probably the strongest at this point," O'Mara said, for three reasons.
First is the fact the state's law says a person has "no duty to retreat."
Second: the state's law provides immunity from criminal prosecution and civil actions, O'Mara said, "which not all other 'stand your ground' statutes do."
The final reason, O'Mara said, can be attributed to a recent change in the law, which shifts the burden onto the state to prove that a shooter did not act in self-defense and is therefore not entitled to "stand your ground" immunities.
Previously, the shooter used "stand your ground" as a defense, and had to prove she or he feared further bodily harm. But no longer.
"Nowhere else is there anything like this in criminal law where somebody asserts something and the burden then shifts to the other person," Pinellas County Sheriff Bob Gualtieri said in a press conference. "That's a very heavy standard and it puts the burden on the state."
Florida's law has drawn attention over the years, most notably in the shooting death of 17-year-old Trayvon Martin in Sanford, Florida.
In 2012, a jury found George Zimmerman -- who O'Mara represented in that case -- not guilty in the shooting death.
Martin was walking to his father's fiancee's house from a convenience store when Zimmerman, a neighborhood watch volunteer, saw him and called the police. Zimmerman defied an order to not approach the teen. When he did, the two got into a physical altercation, and Zimmerman shot Martin.
As the case garnered national attention, onlookers speculated whether Zimmerman would try to use the Florida's "stand your ground" law as part of his defense.
Zimmerman was charged in Martin's death but was eventually acquitted. Ultimately, he did not lean on the state's "stand our ground law," but did claim self defense.
Still, the case cast a spotlight on Florida's "stand your ground" law and demands to change it.
Why it's a controversial issue
Supporters of "stand your ground" laws say they give people the right to protect themselves. Former Florida Gov. Jeb Bush defended the law at the National Rifle Association's 2015 annual meeting in Nashville.
"In Florida you can defend yourself anywhere you have a legal right to be," he said. "You shouldn't have to choose between being attacked and going to jail."
The NRA has pushed hard for "stand your ground" laws in the past. Its former president, Marion Hammer, helped create Florida's law back in 2005.
Critics say the laws encourage violence and allow for legal racial bias. In 2013, Sherrilyn Ifill, then president and director-counsel for the NAACP Legal Defense & Educational Fund, gave testimony in a hearing on "stand your ground" laws.
"Even those who do not consciously harbor negative associations between race and criminality are regularly infected by unconscious views that equate race with violence," she wrote.
Racial stereotypes, she wrote, could cause people to misinterpret innocent behavior as something threatening or violent, and "stand your ground" laws could justify this violence.
With the controversy surrounding "stand your ground" laws, there have been efforts to change or repeal them. In 2017, North Carolina lawmakers filed the Gun Safety Act, which would repeal the state's "stand your ground" law. No updates on the bill have been available since April of 2017.
The NCSL says recent attempts have not been successful.
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