Keyshawn Johnson & Justin Bieber Feud

Justin Bieber has a pat defense these days ... as in, "I'm being framed," and we've learned that's exactly how he's attacking 2 criminal investigations targeting him.

CRIMINAL CASE #1:

The L.A. County District Attorney is currently deciding whether to prosecute Bieber for allegedly spitting in a neighbor's face and threatening to kill him after the neighbor confronted the singer for driving his Ferrari at breakneck speeds in the neighborhood.

Law enforcement sources tell us ... Bieber's people have told the D.A. they have a witness who will swear under oath ... Justin didn't spit. Our sources say the D.A. will not make a decision until they're able to interview the witness. FYI ... law enforcement sources tell us they have at least one witness -- aside from the alleged victim -- who will testify he saw the Biebs spit in the guy's face.

CRIMINAL CASE #2:

As we first reported ... Justin's being investigated for reckless driving after allegedly racing his white Ferrari Monday night on the streets of his gated community. Sources connected with the singer are quietly floating the defense that Justin was not driving.

Here's the problem. We broke the story ... Keyshawn Johnson chased Bieber down in his Prius and then blocked his driveway. We're told Keyshawn actually ran up the driveway into the garage and eyeballed Bieber jumping out of the car and running into the house. Law enforcement also tells TMZ ... multiple witnesses "clearly saw" Bieber driving the car.

We're told the L.A. County Sheriff's Dept. will refer the latest Ferrari case to the D.A. shortly. If things keep up, the D.A. is gonna need a special Bieber prosecutor.

Keyshawn Johnson is still furious with Justin Bieber -- claiming the pop star is "playing with dynamite" by endangering Keyshawn's family with his reckless driving.

TMZ spoke with Keyshawn's agent Jerome Stanley who tells us ... Keyshawn is "very, very, very livid" with Justin for blazing through their Calabasas community in his Ferrari on Monday ... right where Keyshawn was walking with his children.

As we previously reported, Keyshawn chased after Bieber in his Prius -- and tried to confront the singer at Bieber's house -- but JB ran and hid inside of his home when Key pulled up.

"Keyshawn is taking the situation very seriously," Stanley says ... "He wants Justin to slow down and be a responsible neighbor."

Cops received multiple phone calls from concerned neighbors reporting Justin's dangerous driving -- and now the L.A. County Sheriff's Dept. has launched an investigation into the matter.

We asked Stanley if Keyshawn plans to aid in the investigation -- to which he replied, "Keyshawn is a law-abiding citizen and he'll do whatever it takes to help the authorities."

When Justin Bieber allegedly raced his Ferrari past ex-NFL stud Keyshawn Johnson ... he learned a valuable lesson -- never underestimate an angry man in a Prius!

Especially one way bigger than you.

NFL Hall of Famer Eric Dickerson says he's personally witnessed Justin Bieber racing his Ferrari around the streets of Calabasas ... and tells TMZ he's worried the singer could seriously hurt someone if he doesn't slow his ass down.

We spoke to Dickerson -- who's lived in Calabsas for years -- and the NFL legend tells us he doesn't blame Keyshawn Johnson for confronting the singer yesterday.

"I've seen [Justin] driving fast around Calabasas before in the Ferrari," Dickerson says ... "It's just not safe."

Dickerson says he owns two Ferraris and understands how dangerous the car can be if an irresponsible person happens to be in the driver's seat.

"I used to drive fast," Dickerson admits ... "but that was on the freeway ... and even that wasn't safe."

As for Keyshawn's decision to follow Bieber to his home, Dickerson says -- "I don't blame Keyshawn, he's got kids ... I don't blame him for trying to get [Justin's] attention."

"I would've been the same way ... when you're a father it takes on a whole new meaning. Plus, we got that football mentality."

Keyshawn Johnson chased down a speeding Justin Bieber this weekend -- and tried to confront the singer about his dangerous driving habits -- but JB ran away like a scared little child ... eyewitnesses tell TMZ.

Sources tell us ... Keyshawn -- a former NFL superstar -- had just left a party Monday night inside of his exclusive gated community in Calabasas (with his child in the car), when Bieber zoomed by in his Ferrari at breakneck speeds.

We're told Keyshawn was furious -- feeling Justin could've killed someone -- so he brought his kid home, then chased after the singer in his Prius (yes, a Prius chasing a Ferrari).

When KJ got to Bieber's pad -- he blocked Justin's Ferrari in the driveway and got out of his car to confront Justin face-to-face ... but Justin ran inside of his house and refused to come out.

FYI -- Keyshawn is 6'4", 212 lbs ... Justin's about 5'7", 110 lbs (soaking wet).

As we previously reported, at least 2 people called the police on Justin that night -- and cops responded to the singer's home.

There's more ... sources say SEVERAL people witnessed the speeding incident -- and say Justin was definitely in the driver's seat. We're told the witnesses told Sheriff's deputies ... Bieber appeared stoned at the time.

We're still waiting to hear from Bieber's camp.

10:15AM PDT Now an NFL Hall of Famer is weighing in ... Eric Dickerson, who also lives in Calabasas, just tweeted ... "Justin Bieber needs to slow his ass down."

Justin Bieber is under police investigation for ANOTHER reckless driving incident -- allegedly driving his Ferrari at breakneck speeds in his gated community.

The incident occurred at around 8 PM Monday night. L.A. County Sheriff spokesman Steve Whitmore tells TMZ ... cops received 2 separate calls in different locations in the Calabasas community. Sources say one of the callers was Keyshawn Johnson.

Whitmore says the callers reported Bieber was driving at a "startling high rate of speed." At least one child was playing in the area where Bieber was allegedly driving.

We're told cops responded but Bieber refused to speak with them.

Bieber has had a history of alleged reckless driving. You'll recall prosecutors are currently reviewing a case where Bieber allegedly drove recklessly and then spit on a neighbor who confronted him. The neighbor says Bieber also threatened to kill him.

As for Sunday's case ... Whitmore says the case will be presented to the L.A. County District Attorney.

We spoke with Bieber's rep -- so far, no comment.