ALLEN PARK, Mich. – Jim Caldwell was happy to have some humidity Saturday afternoon. Football coaches, for multiple reasons, always seem to like that.

It tests the conditioning of players. It tires them out quicker, making the end of practices feel more like the end of games where players have to be able to fight through fatigue to make big plays and win games. It also helps prepare for early-season contests in the heat -- and while the Lions don’t play in any broiling cities early on (at San Diego, Minneapolis and Seattle), it can’t hurt to have some heat.

Here’s what stood out during the warm, crowded public practice Saturday, one that concluded with Dan Orlovsky running around in the sprinklers with his children long after everyone else left the field.

1. Calvin Johnson once again had the play of the day: In a scene fans and those around the NFL have seen time and time again, Johnson took off down the sideline during an 11-on-11 period in practice. Darius Slay had perfect coverage, and it didn’t matter. Matthew Stafford tossed up a perfect pass, and Johnson adjusted his body, jumped up and grabbed the ball before falling to the ground. To give you an idea of how good Johnson has been during this training camp -- he’s been doing this almost daily. As long as he stays healthy, he could be in line for a really strong season.

2. Trying to understand the receiver competition: There is still a large jumble behind Johnson and Golden Tate for the rest of the receiver spots and who wins those jobs likely won’t be determined by receiver play alone. But in receiver-defensive back one-on-ones, Johnson, Tate, Corey Fuller, Jeremy Ross, Ryan Broyles and Lance Moore were the players working with Stafford on Saturday. It might not be something to read into, but the way to tell who could win roster spots could be followed with who works with the starting quarterback. Of course, special teams coverage and returner skills are going to play into this beyond Johnson, Tate and Fuller.

3. Rashean Mathis is just fine: He sat out the preseason opener but was back at practice Saturday and had one of the defensive highlights, timing a pass breakup perfectly on an attempted Stafford-to-Johnson connection. Both he and Darius Slay have had their moments during this training camp, which is a positive sign when facing one of the most seasoned quarterback-to-receiver combinations in the NFL.

4. Nevin Lawson is pushing for a starting gig: Less than a year after a nasty foot injury ended his rookie season after a little under two games, Lawson is really making an impression this camp. He and veteran Josh Wilson have separated themselves from rookie Quandre Diggs at this point, and while all three figure to make the roster, Lawson is putting himself in position to win the job. He has worked with the first team often throughout camp and has shown versatility on the outside when necessary as well. He’s probably still a little small to be a dependable backup outside corner, but he’ll need to play inside and outside if he’s going to be on the field. After practice, Caldwell cited his toughness and tenacity when asked about him.

5. The injured guys are still working: Not a huge update here, although Joique Bell continues to look like he is making positive progress toward a return soon. Jason Jones did some more working out Saturday, and LaAdrian Waddle continued to push and hit the sled. Watched Alex Carter run a little bit, too. He still looks somewhat slow, but he was also running around hula hoops, so he was working some other movement as well. The only player I have not seen with much side work is Haloti Ngata. Joseph Fauria, who returned to practice Saturday.