SAN DIEGO -- It’s been an eventful offseason for San Diego Chargers receiver Keenan Allen.

Just check Allen’s Instagram account for all of the quirky details. He spent a day with friends at Disneyland, caught passes from Johnny Manziel while the quarterback trained for the draft here in San Diego, attended good friend Cincinnati receiver Marvin Jones' wedding and sat courtside to watch his favorite NBA star, LeBron James, perform against the Charlotte Hornets back in Allen’s home state of North Carolina -- all in the span of about two months.

“He takes his work serious, and he has a lot of pride in what he does,” Allen said about Manziel. “And I have a lot of respect for what he does. I respect his game.”

Of course, this offseason hasn't just been about Kodak moments for Allen. The Cal product also put in extensive work getting stronger and faster in the weight room and on the practice field, preparing for an encore performance to an impressive rookie season.

Allen is out to show doubters he’s not just a one-hit wonder, and his production during a magical rookie season wasn't a fluke.

“One thing for him that’s going to be key -- and I think he knows this -- is not to relax and think you’re going to just duplicate that year,” Chargers quarterback Philip Rivers said. “They’re going to know where No. 13 is, have a plan for him and try to take away the things he does well.”

Rivers said it will be important for Allen to focus on doing the small things well in order to improve in his second season. And Rivers believes his new No. 1 receiver has the right mindset.

Allen said a primary focus has been improving his speed. One reason Allen dropped to the third round in the 2013 draft is that he ran a slow time in the 40-yard dash at his pro day. Still recovering from a knee issue that cut short his final season at Cal, Allen was timed at about 4.65 seconds.

Allen believes he is faster now and fully healthy.

“I mean if you run a 4.3 or 4.4, that obviously says that you're fast,” Allen said. “But a 4.6 guy can still make their way into the league. Some of the best receivers in the league ran a 4.5 or 4.6. So now that I'm healthy, I'm pretty sure I'm faster than 4.6.”

Chargers general manager Tom Telesco benefited from doing his homework, evaluating Allen in person and on film, and understanding how he consistently created separation to make big plays.

“His route-running [stood out],” Telesco said, when asked to provide one trait in the evaluation of Allen that would translate to the league. “Not only his quickness getting in and out of breaks, but his feel for it.”

Chargers offensive coordinator Frank Reich says Allen’s ability to make people miss at his size -- 6-foot-2 and 211 pounds -- makes him special.

“He has great wide receiver qualities,” Reich said. “He’s great off the line of scrimmage against press. He’s got great feet. He’s really good with the ball in his hand. You just ask him to keep building on what he did last year.

“From the fifth game on, he literally was a Pro Bowl-caliber player in his rookie year. He was phenomenal. Now, it’s all about consistency. Can you do it year in, year out?”

Keenan Allen took to the air to score a TD in an important December road win against Denver. Joe Amon/The Denver Post via Getty Images

Allen could have missed out on the opportunity to shine during his rookie season. Still working his way back from the knee injury, he was mired near the bottom of San Diego’s depth chart behind Danario Alexander, Malcom Floyd, Eddie Royal and Vincent Brown during training camp.

Struggling to pick up the offense and unfamiliar with how to handle not being the go-to guy, Allen became frustrated with his lack of playing time and contemplated leaving the team to pursue his other love -- music.

Allen had been singing in the church choir since he was a child, and he also taught himself how to play the piano. He and childhood friend Kenae Stokes spent time in the recording studio and produced a song, with a tentative title “Start the Party.”

But fate conspired to provide Allen with that opportunity to play, as Alexander and Floyd suffered season-ending injuries early last season, forcing Allen into a starting role.

“It was serious to the extent that I was talking to my mama -- and not anyone else,” Allen said about his contemplation of moving on from football. “It was just a thought. I just thought I wanted to do something else. She just told me to stick with it.

“Football is my love, my life. And I just kept playing. Unfortunately those injuries happened, and I was able to make my mark.”

Allen thrived as a starter, leading all rookies in 2013 and setting a team record with 1,046 receiving yards and 71 catches during the regular season. He became the fifth rookie since 2000 to eclipse 1,000 receiving yards, and he was just as effective in the postseason, finishing with eight catches for 163 yards and two touchdowns.

Allen proved to have a nose for the end zone, with eight touchdowns. His signature moment was a 19-yard touchdown on a drag route in a big win at Denver during the regular season. He jumped over defensive back Kayvon Webster and ran over safety Mike Adams to get into the end zone for the score.

A running back in high school, Allen had a growth spurt heading into his junior season, growing from 5-9 to 6-2. That growth spurt led to a change of position from running back to receiver. But Allen kept those instincts for running the football.

He should benefit from the return of Floyd. The 6-5, 225-pound receiver has been a surprise addition for the Chargers, returning from a serious neck injury and looking like his old self during offseason work.

The two receivers forged a strong bond, often getting together to play video games at Allen’s house.

“Malcom is definitely a go-to guy,” Allen said. “He’s one of the best athletes on the team. He’s tall. He’s fast. He’s quick. It’s kind of hard for a DB to get position on him because he’s so big. Just the way he goes out there every day, he works hard and makes plays. He’s just a motivational guy for me.”

While he’s ready to show what he can do on the field come September, Allen is not taking anything for granted. He says he has to once again earn his spot among a talented group of receivers.

“Vincent comes out and has a great practice almost every day,” Allen said. “He puts in work, so it’s real hard to compete with that. Not taking anything from Malcom or Eddie, but Vincent really stands out with his routes and stuff like that.

“There’s always competition. Nobody ever has their guaranteed spot, except for maybe Philip and Antonio Gates.”