The 49ers are going to rely on cornerbacks to hold up in man coverage in new coordinator Jim O’Neil’s defense. He said this offseason part of his defense’s “mantra” is to confuse and hit the quarterback.

That means varying looks along the defensive front and relying the secondary to blanket receivers with variations of press and zone coverages.

“We’re going to find ways to get after the quarterback, whether it’s three, four, five, six, seven guys if we have to, because if you let quarterbacks be comfortable in the pocket, it’s hard to win,” O’Neil said.

To fit that bill, the 49ers used a fourth-round pick in the recent NFL draft on embattled cornerback Rashard Robinson, who dealt with a series of off-the-field issues at LSU that caused his draft stock to fall despite promising physical gifts.

Related Ranking the 49ers five best offseason additions

Robinson (6-foot-1, 177 pounds) ran a 4.40-second 40-yard dash at his pro day. His combination of length and explosiveness is emblematic of a player worthy of an early-round selection. He’s faster and has longer arms than Richard Sherman, who’s become the archetype for corners of Robinson’s ilk.

But Robinson’s suspension as a sophomore, and an arrest last summer for unauthorized entry into a teammate’s apartment (charges were dropped), led to virtually getting kicked off the team last season. He decided to enter the draft instead of transferring to another program.

At the time of his selection, there were plenty of questions about general manager Trent Baalke’s decision to add Robinson to a crowded group of cornerbacks. The 49ers in 2014 drafted four corners – including nickel back Jimmie Ward – who were still cutting their teeth in the NFL. Adding Robinson, along with third-round pick Will Redmond, seemed unnecessary on a roster needing to infuse talent on other areas.

But after watching Robinson during the offseason program, it’s clear why Baalke was enamored with what he could do on the field. Robinson is fiery and competitive, and looks like a starter in the making. He has the talent to become the team’s top corner with time and development.

Related Former 49ers head coach Jim Harbaugh stars in familiar rap video

With training camp starting July 31, Tramaine Brock and Jimmie Ward appear to be the starters at corner. Ward spent the spring and June’s minicamp learning the right corner position with the first-team base defense in order to play all of the snaps after playing roughly 65 percent of downs last season. It remains to be seen if Ward will kick inside to the slot in sub packages, as he did during his first two years.

If he does, Robinson will be in position to compete for time as the third cornerback, with 2014 picks Kenneth Acker, Dontae Johnson and Keith Reaser.

Robinson has the most upside of the bunch, giving him a great chance to earn a prominent role as a rookie in O’Neil’s aggressive defense. He has the skill set on the outside O’Neil needs if he’s going to creatively dial up pressure on opposing quarterbacks.

But Robinson must mature and prove his issues that plagued his college career are in the past.