12:32 PM PT -- YG's bail has been set at $250,000.
11:14 AM PT -- Tacopina tells TMZ, YG has been arrested on suspicion of robbery based on an ongoing investigation. He says, "This has become even more outrageous ... normally, in the American justice system, you get arrested after an investigation is completed. The motives here are pretty clear."
11:06 AM PT -- YG has recruited powerhouse attorney Joe Tacopina, who tells us, "This arrest is one that caught YG completely off guard because there is no truth to them. YG has no idea what investigators are talking about and we have not been provided with any details ... we are learning about this case through the media."
Tacopina continues, "Rest assured, my client will be cleared of all charges, if they even survive past the arraignment."
Tacopina also raises questions about the motive and timing of the arrest, saying, "YG has a performance scheduled at The Grammy's Sunday where he will honor Nipsey Hussle ... so the timing is suspect, to put it mildly."
YG's friend and fellow rapper, The Game, also seems to have some questions about the timing of the bust ... taking to Twitter to express his concerns.
9:32 AM PT -- Cops now have YG in custody, and law enforcement sources tell us he's being transported to a jail to be booked for robbery.
YG's Friday is off to a troubling start -- cops showed up on his doorstep before sunrise armed with a search warrant ... TMZ has learned.
Law enforcement sources tell us L.A. County Sheriff's deputies arrived at the rapper's San Fernando Valley home around 4 AM, and they're still there now. YG is home, and we're told they have a search warrant and an arrest warrant related to a robbery case.
Of course, YG's SUV was recently connected to a murder case. We broke the story ... the L.A. County Sheriff's Dept. says it's close to cracking the case, but has asked the public for an assist. As we told you, the rapper's Escalade was involved in a high-speed chase back in July through L.A. streets -- and it ended with someone in the vehicle shooting and killing a 65-year-old man on a bicycle.
YG told us at the time ... "I was nowhere near the scene of this incident and had been in a recording studio all day in Hollywood. I was there until after midnight on the Fourth of July and didn't learn of these events until after they happened."
It's unclear if the Friday morning raid is related to that case.
A couple weeks after the shooting, a Hollywood Hills home leased by YG was raided and at least one person was arrested for a weapons charge. The rapper was not present at the house during that raid.