What happens when an unstoppable baserunning force meets an immovable catching object? The Phillies and Reds gave fans a firsthand demonstration this week, in a series pitting Philadelphia catcher Jorge Alfaro against four-time 50-steal man Billy Hamilton and Cincinnati.
Alfaro has a cannon arm -- in limited 2017 action, he led all catchers in arm strength, averaging 89.8 mph on max-effort throws (MLB average is 81.8 mph), as tracked by Statcast™. His average pop time to second base was 1.95 seconds -- a top-10 mark, better than the 2.01-second MLB average.
But this week, the young backstop was staring down one of the Major Leagues' fastest men. Last season, Hamilton tied with Byron Buxton as the fastest baserunner in baseball by Statcast™'s Sprint Speed metric. He averaged an elite 30.1 feet per second on his max-effort runs, while MLB average is just 27 feet per second. And Hamilton is just the leader of the pack -- Phillip Ervin (29.1 feet per second) and Jose Peraza (28.2 feet per second) are also basestealing threats for Cincinnati who excel in sprint speed.
In the three-game set at Citizens Bank Park, Alfaro and the Reds' speedsters clashed repeatedly in a thrilling series of matchups on the basepaths. Statcast™ was tracking the entire show.
Round 1: Alfaro vs. Ervin, sixth inning, Game 1
Result: Stolen base
Gif: Phillip Ervin steals second base
In the first baserunning matchup of the series, Ervin swiped second base despite a strike from Alfaro. How did Ervin do it? A big lead, coupled with Phils shortstop Scott Kingery being slightly late covering the bag and missing the tag.
Statcast™ info
Ervin's secondary lead: 28.4 feet
Ervin's sprint speed: 28.4 feet per second
Alfaro's pop time: 1.94 seconds
Alfaro's arm strength: 86.0 mph
Round 2: Alfaro vs. Hamilton, sixth inning, Game 1
Result: Stolen base
Gif: Billy Hamilton steals on Jorge Alfaro
The fans in attendance didn't have to wait long for the main event. Hamilton reached on an infield hit in the same inning (with a blazing fast 3.85-second home-to-first time and a 30.6 feet per second sprint speed, exceeding the elite 30-plus benchmark) as Ervin, and then Hamilton wasted no time taking off for second. Alfaro rose to the task, uncorking a monster throw that was perfectly accurate -- but Hamilton was simply too fast.
Statcast™ info
Hamilton's secondary lead: 26.1 feet
Hamilton's sprint speed: 29.9 feet per second
Alfaro's pop time: 1.90 seconds
Alfaro's arm strength: 88.6 mph
Round 3: Alfaro vs. Hamilton, sixth inning, Game 1
Result: Out at home

Alfaro got his first taste of revenge on this one, when two pitches after stealing second, Hamilton tried to score from second on a wild pitch. But Alfaro made a great play to corral the ball near the backstop and zip a throw home (although there was no arm strength reading) to catch Hamilton just in the nick of time.
Statcast™ info
Hamilton's sprint speed: 29.5 feet per second
Round 4: Alfaro vs. Peraza, seventh inning, Game 1
Result: Stolen base
An inning later, Peraza got his turn to run. Alfaro's throw to second was again strong, but this time was less accurate -- low and into the basepath -- and it skipped past Kingery and Maikel Franco into center field.
Statcast™ info
Peraza's secondary lead: 23.8 feet
Peraza's sprint speed: 31.0 feet per second
Alfaro's pop time: 1.86 seconds
Alfaro's arm strength: 88.6 mph
Round 5: Alfaro vs. Hamilton, third inning, Game 2
Result: Stolen base

On to the second game of the series. Hamilton walked in the top of the third, and after five pickoff attempts by Aaron Nola, the speedster took off. Like in the series opener, Alfaro met Hamilton's peak speed with peak arm strength, and his throw was accurate. But once again, Hamilton's speed simply won the battle.
Statcast™ info
Hamilton's secondary lead: 24.5 feet
Hamilton's sprint speed: 29.9 feet per second
Alfaro's pop time: 1.91 seconds
Alfaro's arm strength: 88.9 mph
Round 6: Alfaro vs. Hamilton, fifth inning, Game 2
Result: Stolen base

Hamilton was the clear winner here. After walking again -- and another three pickoff throws -- he stole second cleanly, with Alfaro's throw one-hopping in late.
Statcast™ info
Hamilton's secondary lead: 23.2 feet
Hamilton's sprint speed: 29.8 feet per second
Alfaro's arm strength: 84.3 mph (no tracked pop time)
Round 7: Alfaro vs. Peraza, fifth inning, Game 2
Result: Bunt groundout
Peraza tried to bunt for a hit with two outs, but Alfaro got out from behind the plate quickly to pounce on the ball, and he even had time to take something off for an accurate throw to get the out.
Statcast™ info
Peraza's sprint speed: 29.6 feet per second
Peraza's home-to-1st: 3.90 seconds
Alfaro's arm strength: 74.0 mph
Round 8: Alfaro vs. Hamilton, third inning, Game 3
Result: Groundout
Gif: Jorge Alfaro throws out Billy Hamilton at first
This was a terrific play by Alfaro. Hamilton chopped a ground ball off home plate and high into the air, and he was burning down the line toward first as Alfaro waited for it to come down. With no time to spare, the Phillies catcher released a rocket to first just in time to get the out.
Statcast™ info
Hamilton's sprint speed: 30.2 feet per second
Hamilton's home-to-1st: 4.00 seconds
Alfaro's arm strength: 85.6 mph
Round 9: Alfaro vs. Peraza, sixth inning, Game 3
Result: Stolen base
Peraza successfully ran on Alfaro for a second time in the sixth inning of the series finale. Alfaro's pop time was again exceptional, but his throw was a little high, leaving Franco unable to get a tag down in time.
Statcast™ info
Peraza's secondary lead: 23.0 feet
Peraza's sprint speed: 28.9 feet per second
Alfaro's pop time: 1.83 seconds (no tracked arm strength)
Round 10: Alfaro vs. Ervin, 11th inning, Game 3
Result: Caught stealing

This was the last baserunning duel of the series -- and Alfaro saved his best for last, making a big-time play to keep the go-ahead run out of scoring position in a tie game in the 11th inning. Ervin took off on a breaking ball from Edubray Ramos, but even with the slow pitch, Alfaro got rid of the ball extremely fast, and his laser throw just to the first-base side of the bag allowed shortstop J.P. Crawford to slap down a tag just as Ervin slid in. The Phils would go on to win the game an inning later.
Statcast™ info
Ervin's secondary lead: 21.9 feet
Ervin's sprint speed: 28.3 feet per second
Alfaro's pop time: 1.92 seconds
Alfaro's arm strength: 86.6 mph