When the St. Louis Rams spent two picks, including a second-rounder, on running backs during the 2012 NFL Draft, it seemed clear that for the first time the team was making plans for a day when Steven Jackson would no longer be its lead back.

Nobody thought that day might be in 2012.

Dramatic, yes, but it’s not hard to see a day in the near future when rookie RB Daryl Richardson is getting the lion’s share of the carries in the Rams offense. On Sunday, Richardson received 11 carries to Jackson’s 10 and rushed for 76 yards, besting Jackson’s 52.

It’s not just Richardson’s effectiveness that has raised questions, though. In fact, Richardson’s emergence has just served as fuel to the fire that began when news leaked out before the Rams’ Thursday night game against the Arizona Cardinals that Jackson had his contract restructured in the offseason to allow him the option to become a free agent after the 2012 season.

The news was more shocking than surprising. There are plenty of reasons both sides would agree to such a deal, making it unsure which party even initiated such a discussion. But whichever side asked for it, the fact remains: Jackson’s time in St. Louis may be limited.

For his part, Jackson has remained steady in his desire to be a member of the Rams.

“It’s a part of the business,” Jackson said after the Cardinals game. “I’ve said that from the beginning that, even in 2004, I wanted to retire here. This organization gave me the opportunity to live out a dream. In 2008 they extended me and at the end of the season we’ll see what happens with me. But something is happening here and I want to be a part of it.”

There are factors working against Jackson, though. The biggest may simply be his age – it’s well documented that running backs tend to begin to decline around the age of 30, which Jackson will turn next July. Jackson is also slated to make $7 million next season, a figure that would put him behind only Minnesota’s Adrian Peterson and Tennessee’s Chris Johnson in terms of salary. And he’s struggled to stay healthy recently, often dealing with small injuries that hinder his effectiveness.

Another factor working against Jackson is the young Richardson. The seventh-round pick out of Abilene Christian has been a revelation in his short time with the Rams, averaging 5.2 yards per carry and breaking runs of 53 and 44 yards in recent weeks. Richardson has been the proverbial lightning to Jackson’s thunder, and in many cases it’s the lightning that has put on the better show.

“He’s a change of pace to what people are used to with ‘Jack’ carrying the football,” Rams coach Jeff Fisher said. “He’s got great acceleration speed and he’s going to be a playmaker for us.”

There are certainly ways this doesn’t end in a messy divorce, and although he’s been terrific nobody is ready to anoint Richardson as the next Rams workhorse. Lightning still does need its thunder, after all, and Jackson has been as thunderous a back as there is in the league for years. Jackson may not be running out of time in St. Louis just yet. But it seems much more clear that the clock is ticking.