KANSAS CITY, Mo. -- The last time quarterback Alex Smith played against the St. Louis Rams, in 2012, his career took an abrupt turn. He received the concussion that kept him out of the San Francisco 49ers lineup and gave his team the excuse to bench him permanently in favor of Colin Kaepernick.

That precipitated last year's trade that sent him to the Kansas City Chiefs, where Smith is now the starter and will face the Rams again on Sunday at Arrowhead Stadium.

The game is another in a reunion tour of sorts for Smith. The Chiefs played in San Francisco three weeks ago. They met the Chargers last week in San Diego, Smith's hometown.

Now it's a more painful memory. Smith after a running play fell awkwardly and was hit in the back of the head by St. Louis linebacker Jo-Lonn Dunbar. That was, other than a lone pass attempt in a meaningless game at the end of the season against Arizona, for all intents ahnd the end of Smith's San Francisco career.

Smith was reluctant this week to speculate where his career might be now if not for the concussion. He merely said, "I remember the game, remember it well."

His benching and replacement with Kaepernick was probably inevitable. The 49ers had drafted Kaepernick a year earlier and he was bound to eventually become a starter.

Smith's injury gave the 49ers their reason. Not surprisingly, Smith since joining the Chiefs has shown an affinity for the feet-first slide when he runs. Otherwise, Chase Daniel could get a promotion like Kaepernick did in San Francisco

"You get a little bit smarter," Smith said. "Whether you like it or not, you're a quarterback and you're a target and you get outside the pocket some of the rules that are there to protect you go away. So it's [about] being smart with it, being smart, understanding situations and for the most part protecting yourself when you do get outside the pocket."